AMERICAN 
TELEGRAPH  PRACTICE 


McGraw-Hill  Book  Company 


Electrical  World         The  Engineering  andMining  Journal 
En5ineering  Record  Engineering  News 

Railway  Age  G  azette  American  Machinist 

Signal  kngin<?<?r  American  Engneei- 

Electric  Railway  Journal  Coal  Age 

Metallurgical  and  Chemical  Engineering  Power 


AMERICAN 
TELEGRAPH  PRACTICE 


A  COMPLETE  TECHNICAL  COURSE  IN  MODERN 

TELEGRAPHY,  INCLUDING  SIMULTANEOUS 

TELEGRAPHY  AND  TELEPHONY 


BY 
DONALD  McNICOL,  A.  M.,  A.  I.  E.  E. 

MEMBER   OP   THE    ENGINEERING   STAFF,    POSTAL  TELEGRAPH-CABLE 
COMPANY,    NEW   YORK 


McGRAW-HILL   BOOK   COMPANY 

239  WEST  39TH  STREET,  NEW  YORK 

6  BOUVERIE  STREET,  LONDON,  E.  C. 

1913 


COPYRIGHT,  1&13,  BY  THE 
McGRAW-HiLL  BOOK  COMPANY 


THE. MAPLE. PRESS. YORK- PA 


PREFACE 

In  this  work  the  aim  has  been  to  give  a  detailed  exposition  of  the  various 
systems  of  telegraphy  in  use  in  America  at  the  present  time,  together  with  a 
complete  description  of  modern  methods  of  operation,  and  an  extensive 
compilation  of  the  formulae  used  in  practical  telegraphy. 

One  occasionally  hears  it  remarked  that  since  the  practical  introduction 
of  the  quadruplex  about  thirty  years  ago  there  have  been  no  important 
developments  in  telegraphy,  but  those  who  have  been  engaged  in  the  work 
of  improving  telegraph  apparatus  and  operating  methods  are  well  aware 
that  even  since  the  last  American  book  dealing  with  this  subject  was  written 
several  years  ago,  material  progress  has  been  made  in  several  directions. 

The  fact  that  to-day  eighty  telegrams  per  hour  are  handled  over  a  single 
Morse  outlet  where  ten  years  ago  half  that  number  in  the  same  time  was 
considered  good  performance,  and  that  during  the  same  period  the  time  of 
transmission  of  a  telegram  between  cities  remotely  separated  has  been  reduced 
at  least  one-half,  cannot  but  be  regarded  as  convincing  evidence  that  vast 
improvement  has  taken  place. 

One  factor  that  has  contributed  largely  to  the  improvement  in  the 
service  is  the  increasing  technical  knowledge  of  the  men  engaged  in  operating 
the  plant;  and  this,  in  spite  of  the  fact  that  the  production  of  technical 
telegraph  literature  has  not  kept  pace  with  the  actual  development  of  the  art. 

In  the  present  work  the  author  has  incorporated  all  of  the  elemental 
essentials  of  the  general  subject  as  well  as  all  of  the  new  departures  which 
have  made  for  betterment,  and  an  attempt  has  been  made  to  treat  the  various 
divisions  of  the  subject  in  terms  that  should  make  it  possible  for  the  student, 
by  due  exercise  of  diligence,  to  qualify  himself  for  the  most  advanced  positions 
in  the  service. 

Incidentally,  it  might  here  be  stated  that  it  is  no  longer  possible  for  the 
telegrapher  to  make  much  headway  in  the  service  without  an  understanding 
of  arithmetic  and  elementary  algebra,  and,  while  usually  mathematical 
formulae  are  regarded  as  being  incomprehensible,  by  those  who  have  not 
had  the  advantages  of  high  school  education,  the  author  believes  that  as 
herein  employed  and  worked  out,  all  of  the  required  mathematics  may  be 
mastered  without  difficulty.  The  text  of  the  work  is  based,  to  a  large  extent, 
upon  a  series  of  lectures  given  in  the  evening  technical  schools  in  connection 
with  Columbia  University,  New  York,  during  the  past  year,  and  as  none  of  the 
students,  all  of  whom  are  telegraph  and  telephone  workers,  had  unusual  diffi- 
culty in  understanding  the  mathematics  of  the  subject,  it  is  believed  that  the 

263701 


vi  PREFACE 

problems  submitted  in  the  present  work  will  be  found  no  more  difficult  to  the 
average  student  of  telegraphy. 

The  fact  that  the  controlling  telephone  interests  have  recently  obtained 
control  of  one  of  the  large  telegraph  companies  indicates  that  it  is  realized 
that  the  telegraph  will,  in  all  probability,  remain  for  a  long  time  to  come  the 
only  available,  practicable  means  of  taking  care  of  the  greater  share  of  long 
distance  traffic.  Joint  operation  of  lines  for  telephone  and  telegraph  pur- 
poses simultaneously  is  being  extensively  practiced,  and  that  portion  of  the 
present  work  dealing  with  the  complementary  operation  of  the  two  estab- 
lished methods  of  communication  describes  the  latest  approved  appliances 
and  circuit  arrangements  from  a  telegraphic  standpoint. 

In  deciding  upon  the  subject  matter,  care  has  been  taken  not  to  omit  any 
of  the  features  with  which  operators,  wire  chiefs,  quadruplex  attendants  and 
repeater  attendants  are  concerned. 

The  chapter  on  circuits  and  conductors  illustrates  in  detail  the  principles 
and  laws  of  each  form  of  electric  and  magnetic  circuit  used  in  telegraphy. 

The  chapter  dealing  with  speed  of  signaling  contains  mostly  new  matter 
of  the  greatest  importance  in  maintaining  reliable  high  speed  telegraph 
operation,  while  other  chapters  describe  the  latest  types  of  duplex,  quad- 
ruplex, and  automatic  equipment  used  by  the  Postal  Telegraph- Cable 
Company,  the  Western  Union  Telegraph  Company  and  the  larger  rail- 
road telegraph  systems,  also  up-to-date  methods  of  circuit  concentration 
in  large  offices. 

D.  McN, 
NEW  YORK 

April,  1913. 


INTRODUCTION 

Although  the  nature  of  electricity  is  not  definitely  known,  several  different 
theories  have  been  advanced  by  physicists  within  the  past  century  and  a  half, 
with  the  object  of  attempting  an  explanation  of  the  causes  of  the  various 
phenomena  which  are  called  electrical. 

Most  of  the  old  ideas  relating  to  the  nature  of  matter  have  been  abandoned 
within  comparatively  recent  years.  It  is,  for  instance,  now  believed  that 
matter  is  not  inert,  but  that  in  all  probability  it  is  endowed  with  potential 
energy. 

Present  knowledge  points  to  the  conclusion  that  the  all-pervading  ether  is 
in  some  manner  saturated  with  energy,  available  for  employment,  however, 
only  through  the  agency  of  matter,  which  transforms  it  into  familiar  forms  of 
energy  such  as  heat,  electricity,  etc. 

The  electromagnetic  theory  of  light,  now  generally  accepted,  teaches  that 
energy  from  the  sun  travels  through  the  intervening  ether  to  the  earth  in  the 
form  of  ether  waves.  Thus,  when  it  is  considered  that  most  of  the  natural 
energy  at  our  command  could,  through  the  properties  of  heat,  light,  and  other 
effects,  have  been  identified  as  electrical  energy  in  one  stage  of  its  transfer — 
through  the  ether — the  natural  hypothesis  which  suggests  itself  is  that  the 
etherjs  the  seat  of  electrical  forces.  Indeed,  the  relationship  existing  between 
the  ether  and  what  is  termed  electricity  is  so  close  that  it  would  seem  that  no 
hypothesis  can  be  regarded  as  ultimate  which  does  not  identify  them  as  one  and 
the  same  thing. 

Modern  physical  research  has  brought  together  a  large  number  of  pre- 
viously isolated  facts  which,  placed  in  order  and  logical  sequence,  have  built 
up  that  comprehensive  conception  of  electrical  action  known  as  the  "Electron 
Theory." 

The  atom  is  no  longer  regarded  as  an  absolute  unit.  It  is  now  commonly 
believed  that  the  hydrogen  atom,  for  instance,  is  in  reality  an  atomic  system 
made  up  of  a  thousand  or  more  electrons. 

Spectrum  analysis  of  metals  shows  that  the  hundreds  of  visible  lines  repre- 
sent different  rates  of  vibration  acting  within  the  unit  atom.  In  other  words, 
the  atom  consists  of  a  thousand  or  more  parts,  each  capable  of  independent 
action,  these  parts  being  called  corpuscles  or  electrons. 

Electrons  are  believed  by  some  physicists  to  consist  of  ether.  It  is  assumed 
that  at  rest  electrons  are  spherical  in  shape;  in  motion  their  shape  may  be 
somewhat  distorted,  and  at  high  velocities  they  probably  take  on  the  form  of 
a  disk.  It  has  been  demonstrated  that  each  electron  carries  a  definite  negative 

vii 


viii  INTRODUCTION 

electric  charge,  measurable  in  conventional  electromagnetic  and  electrostatic 
units. 

In  view  of  the  belief  that  electrons  are  constituted  of  ether  it  is  conceivable 
that  in  a  free  state  they  are  present  in  metallic  conductors,  gases,  and  dielec- 
trics, and,  in  a  greater  or  less  degree  in  all  matter;  their  properties,  however, 
being  independent  of  the  specific  properties  of  the  matter  with  which  they 
may  be  associated. 

A  theory  of  electricity  in  order  to  be  of  service  in  experimental  or  practical 
applications  of  electrical  energy  should  account  for  those  manifestations  which, 
for  the  want  of  better  terms,  are  called  positive  and  negative. 

Even  a  moderate  knowledge  of  physics  carries  one  to  a  point  where  the 
electron  theory  is  encountered,  and  this,  opportunely  at  a  stage  where  there  is 
much  need  either  of  experimental  proof  or  of  a  logical  theory. 

If  a  drop  of  water  be  divided  into  a  hundred  parts,  each  separate  part  will 
still  exist  as  water.  Should  the  division  be  carried  to  a  point  where  one  of 
these  minute  droplets  is  separated  into  its  constituent  parts  of  oxygen  and 
hydrogen  we  would  have  then  a  molecule  consisting  of  one  atom  of  oxygen 
and  two  atoms  of  hydrogen.  Further  division  would  separate  the  oxygen  and 
hydrogen  atoms,  and,  as  water,  the  drop  would  cease  to  exist.  The  electron 
theory  presents  an  explanation  of  the  constitution  of  the  atom  itself. 

In  accounting  for  the  manifestation  referred  to  as  positive  electricity, 
according  to  the  electron  theory,  one  might  consider  the  circumstance  of  an 
isolated  atom  consisting  of  a  number  of  electrons  a  trifle  in  excess  of  that 
necessary  to  give  it  proper  atomic  equilibrium.  Should  this  atom  come  near 
to,  or  into  contact  with,  another  atom  deficient  in  its  quota  of  electrons,  a 
transfer  takes  place  which,  in  effect,  establishes  normal  atomic  equilibrium 
so  far  as  these  two  atoms  are  concerned.  It  is  assumed  that  the  first  atom 
would  have  a  positive  electric  charge  and  the  second  a  negative  electric  charge. 

In  the  artificial  generation  of  an  electric  current  such  as  that  due  to  chem- 
ical action,  or  to  electromagnetic  methods,  there  is  brought  about  a  sort  of 
atomic  storm  with  its  accompanying  stresses  and  transfers,  its  ever-contending 
and  colliding  elements  and  its  readjustments  which  are  taken  advantage  of 
and  in  various  ways  employed  as  energy. 

The  propagation  of  electric  energy  from  one  part  of  a  metallic  conductor 
to  another  is  probably  due  to  the  constitution  of  the  metal  so  employed.  The 
atoms  of  the  metallic  element,  the  positive  ions,  being  at  liberty  to  revolve 
about  a  central  point  only,  while  the  negative  electrons  are  free  to  travel  through 
the  mass  of  the  metal,  electric  current  being  due  to  the  locomotion  of  these 
electrons;  passed  on,  as  it  were,  from  atom  to  atom  at  great  velocities. 

Thus  there  is  presented  a  provisional  theory  of  the  nature  of  electricity 
which,  if  not  yet  susceptible  of  lucid  treatment,  at  least  aids  one  in  compre- 
hending the  causes  of  phenomena  with  which  we  have  to  deal. 

Unfortunately  there  is  not  yet  in  vogue  a  terminology  common  to  both 


INTRODUCTION  ix 

theory  and  practice  to  enable  us  in  practical  operations  to  avail  of  the  benefits 
which  might  be  expected  to  accompany  a  clear  understanding  of  advanced 
theory. 

As  a  link  connecting  the  fore-going  brief  statement  of  the  modern  theory 
of  electricity  with  what  is  to  follow  in  succeeding  chapters  in  regard  to  the 
practical  application  of  electrical  energy  we  have  only  to  remember  that  elec- 
tricity in  locomotion  constitutes  current  and  magnetism,  and  that  electricity 
in  vibration  constitutes  light  and  other  forms  of  electromagnetic  radiation. 


CONTENTS 


PAGE 
PREFACE '. ^    ...........       v 

INTRODUCTION .~ vii 

CHAPTER  T 

ELECTRICITY  AND  MAGNETISM  .....    .    .    ....    .  ,  \   ./.•'.    .    ....    .    .    .       i 

•Chemical  Electricity — Magneto  Electricity — Magnetism^—  Relation  between 
Electricity  and  Magnetism — Conductors  and  Insulators — Electric  Potential — 
Electromotive  Force — Resistance — Current — Units  and  Symbols — Definitions  of 
Units. 

CHAPTER  II 

PRIMARY  BATTERIES    .    ...   .    ...    .    .. .    .      ........     n 

Chemicals  Commonly  Employed  and  Their  Symbols — The  Voltaic  Cell — Polari- 
zation—The Gravity  Cell— The  Hydrometer— The  LeClanche  Cell— The  Fuller 
Cell— The  Edison-Lalande  Cell— The  Dry-cell— Standard  Cells— The  Clark  Cell— 
The  Carhart-Clark  Cell— The  Weston  Cell. 

CHAPTER  III 

DYNAMOS — MOTORS — MOTOR-GENERATORS — DYNAMOTORS,  VOLTAGE  AND  CURRENT 

REGULATORS 23 

The  Commutator — Dynamo  "Fields" — The  Ampere-turn — Field  Excitation  of 
Dynamos — Series,  Shunt,  and  Compound  Dynamos — Magnetomotive-torce — The 
Armature — Drum  Winding — Ring  Winding — Closed  Coil,  and  Open  Coil  Arma- 
ture Winding — Lap  Winding — Wave  Winding — Direct-current  Motors — Cu- 
mulative Winding — Differential  Winding — Alternating-  current  motors — Single- 
phase  Series  Motor — Synchronous  Motor — Induction  Motor — The  Stator — The 
Rotor — The  Mo  tor  generator — The  Motor-dynamo — Motor  Current  Regulation 
— Starting  Boxes — Fuses  in  Motor  Circuits — Over-load  and  Under-load  Rheo- 
stats— A.C.  Motor  Starters — Dynamo  Current  Regulation. 

CHAPTER  IV 

STORAGE  BATTERIES — CURRENT  RECTIFIERS;  MERCURY- ARC  AND  ELECTROLYTIC     .     46 
Installation  and  Management  of  Storage  Cells — The  Edison  Storage  Cell — The 
Mercury-arc  Rectifier — Electrolytic    Rectifiers — Management    of    Electrolytic 
Rectifiers— The  Electrodes. 

CHAPTER   V 

POWER-BOARD  WIRING — BATTERY    SWITCHING  SYSTEMS  AND  ACCESSORIES    .    .    .    .58 
Resistance  Units — Bus-bars — Knife  Switches — Western  Union  Dynamo  Arrange- 

xi 


xii  CONTENTS 

PAGE 

ment — Postal  Telegraph  Company's  Dynamo  Arrangement — Three  Wire  System 
— Boosters — Dynamo  Switchboard  Equipment  and  Wiring — Auxiliary  Power- 
boards. 

CHAPTER    VI 

CIRCUITS  AND  CONDUCTORS— THE  ELECTRIC  CIRCUIT— THE  MAGNETIC  CIRCUIT— 

ELECTROMAGNETS .    .    .  • 70 

Ohm's  Law — Battery  Circuits — Divided  Circuits — Cells  in' "Series" — Cells  in 
"Multiple  "—Multiple-series  Connection— Circuit  Calculations— Conductor  Re- 
sistance— Conductance — Specific  Conductivity — Conversion  Factors — Specific 
Resistance,  Relative  Resistance,  and  Relative  Conductivity  of  Conductors — Re- 
sistance Affected  by  Heating — Temperature  Co-efficients — Dimensions  and  Re- 
sistance of  Pure  Copper  Wire — Joint-resistance — Law  of  Shunts — Fall  of  Poten- 
tial— Electrostatic  Capacity  of  Conducting  Wires — Electrostatic  Induction — 
Electromagnetic  Induction — Helmholtz's  Law — Impedance — Inductance — Elec- 
tromagnetism  and  Electromagnets — The  Solenoid — Permeability — Reluctance 
— Hysteresis — Remanence — Time-constant — Practical  Electromagnet  Data. 

CHAPTER  VII 

SINGLE  MORSE  CIRCUITS    . 106 

The  Morse  Circuit— The  Local  Circuit— The  Open  Circuit  System— S  veral  Lines 
Worked  out  of  a  Single  Battery — Single  Line  Instruments. 

CHAPTER    VIII 

LIGHTNING  AND  LIGHTNING-ARRESTERS — FUSES — GROUND   CONNECTIONS      ....   119 
Character  of  Lightning   Discharges — The  Vacuum   Gap   Arrester — The  Brach 
Arrester — The  Choke-coil — Location  of  Lightning-arresters — Pole  ground- wires — 
Fuses — Ground-wires  or  "Earths." 

CHAPTER  IX 

MAIN  LINE  SWITCHBOARDS  FOR  TERMINAL  OFFICES  AND  INTERMEDIATE  OFFICES  .  130 
Classification  of  Offices — The  Strap-and-disc  Board — Switchboard  Connections — 
The  Spring-jack — The  Pin-jack — Terminal  Office  Switchboard  Equipment — Fuse 
and  Arrester  Mounting — The  Cross-connecting  Frame — The  Terminal  Frame — 
Floor  Trenches — Hand-holes — New  Western  Union  Switchboard  Equipment — 
The  Distributing  Frame. 

CHAPTER  X 

ELECTRICAL  MEASURING  INSTRUMENTS— TELEGRAPH  LINE  AND  CIRCUIT  TESTING  .  153 
The  Galvanometer — The  d'Arsonval  Galvanometer — The  Differential  Galvan- 
ometer— The  Ballistic  Galvanometer — Galvanometer  Shunts — Constant  of  a  Gal- 
vanometer— Figure  of  Merit — The  Voltmeter — Hot-wire  Measuring  Instruments 
— Multipliers  for  Voltmeters — Current  Meters — The  Ammeter — Batteries  for 
Testing  Purposes— Chloride  of  Silver  Cells— The  Witham  Battery— The  Wheat- 
stone  Bridge — The  Electric  Condenser — Capacity  of  Condensers — Insulation  Re- 
sistance of  Condensers — Measuring  the  Internal  Resistance  of  Batteries — Earth 


CONTENTS  xiii 

PAGE 

Currents— The  Murray  Loop  Test — Locating  a  "Ground" — Locating  Crosses — 
Correction  for  Lead  Wire  Resistance — Varley  Loop  Tests — Measuring  the  Con- 
ductor Resistance  of  Ground  Return  Circuits — Method  of  Locating  "Opens"  in 
Cables— The  Blavier  Test— Rough  Tests— The  Fisher  Loop  Test— Voltmeter 
Tests — Measuring  a  Ground  Contact — Capacity  Test — Insulation  Resistance 
of  Lines — Various  Methods  of  Measuring  Insulation  Resistance — Conductivity 
Measurements — Locating  Alternating-current  Crosses — Western  Union  Propor- 
tional test  set — Inequalities  in  Line  Resistance — Using  Conductors  of  Mixed 
Gages— Telephone  Receiver  Tests— Testing  Fuses— Fault-finders— The  Math- 
ews  Telafault— The  "Wireless"  Fault-finder. 

CHAPTER  XI 

SPEED  OF  SIGNALING — CIRCUIT  EFFICIENCY      201 

The  Effect  of  Electrostatic  Capacity  upon  Speed  of  Signaling — Retardation — 
Leakage  Conductance — Current  Margin — The  Effect  of  Cabled  Conductors  upon 
the  Speed  of  Signaling — "  Extra"  Currents — Self-induction — Current  Value  of  the 
Stored  Energy  in  the  Magnetic  Field  Surrounding  a  Conductor — KR  Law — Rela- 
tive Telegraph  Transmission  Efficiency  of  Rubber-covered  and  Paper-insulated 
Cables — Telegraph  Speed  in  Words  per  Minute — Signaling  Elements  of  the  Morse, 
and  the  Continental  Alphabets — Semi-automatic  Transmitters — The  Yetman 
Transmitter — The  Vibroplex — The  Mecograph — Speed  of  Signaling  over  Open 
Aerial  Lines — Cross-fire  Effects — Transverse  Leakage — Weather  Cross — Received 
Current  Strength — Receiving  end  Impedance — Relay  Characteristics — Figure  of 
Merit  of  Relays — Importance  of  Accurate  Armature  Suspension — Reducing  the 
Time-constant  of  Receiving  Relays — The  Shunted  Condenser  Method. 

CHAPTER  XII 

SINGLE  LINE  REPEATERS .  ' 219 

Length  of  line  which  may  be  operated  Satisfactorily — The  Effect  of  Resistance, 
Leakage,  and  Capacity  in  Limiting  the  Length  of  Direct  Circuits — Weiny-Phillips 
Repeater— The  Atkinson  Repeater— The  Ghegan  Repeater— The  Neilson  Re- 
peater— The  Toye  Repeater — The  Milliken  Repeater — The  Horton  Repeater — 
Three- wire  Repeater — Self-adjusting  Repeaters — The  d'Humy  Self-adjusting  Re- 
peater— The  Catlin  Permanently  Adjusted  Repeater — Notes  on  Repeater  Adjust- 
ment and  Connections. 

CHAPTER  XIII 

DUPLEX  TELEGRAPHY .    .    .    .    .    .    .    .    .    .    .    .    '*' . 249 

The  Single-current  Duplex— The  Differential  Relay— The  Artificial  Line— Com- 
pensating for  Line  Resistance  and  Line  Capacity — Double-current  Duplex 
Systems — The  Polar  Duplex — The  Pole-changer — The  Polar  Relay — Operation 
of  the  Polar  Duplex — Several  Duplexed  Lines  Worked  from  One  Pair  of  Dynamos 
-"  Closed  "  Pole  and  "  Open  "  Pole  Positions  of  the  Pole-changer  Armature  Lever 
—Gravity  Battery  Duplex— The  Bridge  Duplex— The  Reading  Condenser— The 
Signaling  Condenser — Western  Union  Bridge  Duplex  System — The  High-poten- 
tial Leak  Duplex— High  Efficiency  Duplexes — Duplex  with  Battery  at  One  End 
of  the  Line  Only — City  Line  Duplex — Sparking  at  Contact  Points — Methods  of 
Controlling  the  Spark  at  Transmitter  and  Pole-changer  Battery  Contacts — The 
Johnson  Coil— The  "Make"  Spark. 


xiv  CONTENTS 

CHAPTER  XIV 

PAGBL 

QUADRUPLEX  TELEGRAPHY     .....  287 

"Long  End"  and  "Short  End"  Potentials — Jones'  Quadruplex  System — Booster 
Dynamo  Arrangement  in  Connection  with  the  Jones  Quadruplex — The  Field  Key 
System — "Added"  Resistance  Values — "Internal"  Resistance  Values — "Leak" 
Resistance  Values — Methods  of  Determining  the  Required  Ohmic  Value  of  the 
Resistance  Coils  to  Use  in  the  Field  Key  System  to  Obtain  any  Desired  Propor- 
tions— Resistance  of  Terminal  Apparatus — Resistance  of  the  "Ground"  Coil — 
Operation  of  the  Quadruplex — The  "Postal"  Quadruplex — Single  Dynamo  Quad- 
ruplex— Metallic  Circuit  Quadruplex — The  Neutral-relay  "Kick"  and  the  "Bug- 
trap"  Method  of  Counteracting  its  Effects  upon  Sounder  Signals — The  Repeating 
Sounder— The  Gerritt  Smith  Arrangement— The  Diehl  Bug-trap— The  Differ- 
ential Bug-trap — Bug-trap  Suitable  for  Use  on  Neutral  Side  of  Decrement  Quad — 
The  Condenser  Bug-trap — The  Freir  Self-polarizing  Neutral  Relay — Neutral 
Relays  with  Holding  coils — The  Inductorium — Holding  Coil  of  the  Neutral 
Relay  Employed  in  the  Western  Union  Quadruplex — The  Western  Union  Quad- 
ruplex—The  Neutral  Relay— The  Impedance  Coil— The  Effect  of  the  s-U  Coil 
upon  Outgoing  Currents — Operation  of  the  W.  U.,  Quad — The  Milammeter — 
The  Bitish  Post  Office  Quadruplex. 

CHAPTER  XV 

BALANCING  DUPLEXES  AND  QUADRUPLEXES 331 

The  Resistance  or  Ohmic  Balance — The  Capacity  or  Static  Balance — Timing  the 
Condenser  Discharge — Postal  Telegraph  Cable  Company's  Rules  for  Balancing — 
Western  Union  Telegraph  Company's  Rules  for  Balancing — Approximate  Balances 
— Notes  on  Quadruplex  Operation  and  Management — Line  Capacity  too  High  to 
be  Balanced  with  Total  Capacity  of  the  Condensers — Whether  to  Raise  or  Lower 
the  Compensation  Resistance  in  Order  to  Effect  a  Balance — Negative  Pole  to  Line 
on  Closed  Key — Locating  Faults  in  Duplex  and  Quadruplex  Apparatus — Testing 
the  Condensers — Crossed  Winding  in  Either  Relay — Measuring  the  Distant 
Battery. 

CHAPTER  XVI 

DUPLEX    AND    QUADRUPLEX    "LOCAL"     CIRCUITS — LEG-BOARD    AND    LOOP-BOARD 

CONNECTIONS    .   .   .   , ,   .    .  344 

Methods  of  the  Postal  Telegraph  Cable  Company — Resulting  Circuit  Arrange- 
ments with  the  Levers  of  Both  Local  Switches  Thrown  to  the  Right;  with  Switch 
Levers  to  the  Left;  Switch  Levers  Thrown  "Together,"  Switch  Levers  Thrown 
"Apart" — Branch-office  Control  of  Multiplex  Local  Circuits — Necessary  Con- 
nections where  no-volt  and  where  4o-volt  Dynamos  are  Used  to  Furnish  Current 
for  the  Operation  of  Pole-changers,  Transmitters,  etc. — Loop-switch  Connections 
— Western  Union  Local  and  Loop-switch  Connections — Operating  Table  and 
Branch-office  Wiring — Arrangement  of  Conductors  between  Main  and  Branch 
Offices  — Combination  Single  and  Duplex  Office  Arrangements. 

CHAPTER  XVII 

BRANCH  OFFICE  ANNUNCIATORS— GROUPING    OF  WAY-OFFICE  AND  BRANCH-OFFICE 
CIRCUITS — NEEDHAM     ANNUNCIATOR — OFFICE      SIGNALING     SYSTEMS    FOR 


CONTENTS  xv 

PAGE 
MULTIPLEX  CIRCUITS — BELL  WIRES — MAIN  LINE  CALL  BELLS,  2nd  SIDE  OF 

QUADRUPLEX. — SELECTORS 356 

The  Differential  Annunciator — Annunciator  Board  Connections— Grouping 
Circuits — The  Needham  Annunciator — Multiplex  Bell  and  Lamp  Signaling 
Systems — The  Western  Union  Signaling  System  for  Duplex  and  Quadruplex 
Systems— Main  Line  Call  Bells— Main  Line  "Selector"  Signaling— The  Gill 
Selector — Selector  Connections  for  Single,  Duplex,  and  Repeater  Sets. 


CHAPTER  XVIII 

HALF-SET     REPEATERS — COMBINATION    FULL-SET    AND    HALF-SET     REPEATERS — 
"HOUSE"  REPEATER  CIRCUITS — DUPLEX    AND  QUADRUPLEX    REPEATERS — 

LEASED  WIRE  INTERMEDIATE  "DROPS" 375 

Weiny-Phillips  Half  Repeater — Milliken  Half  Repeater — House  or  Office  Repeater 
Circuits — Multiplex  Repeaters— Quadruplex  Repeaters — Direct-point  Duplex  Re- 
peater— The  "Postal"  Direct-point  Repeater — The  Western  Union  Direct-point 
Repeater — Branch-office  Control  of  Direct-point  Repeater  Local  Circuits — Duplex 
Connected  with  a  Branch  Office  over,  a  Single  Conductor  where  it  is  not  Con- 
venient to  Use  a  Half  Repeater — The  O'Donohue  Shunt  Repeater — Working  an 
Intermediate  Morse  Loop  in  a  Duplexed  Circuit. 

CHAPTER  XIX 

THE  PHANTOPLEX 395 

Superimposing  Alternating  Current  Telegraph  Systems  upon  Existing  Morse 
Circuits — Two  Transmissions  in  One  Direction  Simultaneously  over  a  Single 
Wire — The  Polar  Phanto-quadruplex — The  Phantoplex  Transformer. 

CHAPTER  XX 

HIGH-SPEED  AUTOMATIC  TELEGRAPHY ' 402 

The  Wheatstone  Automatic— The  Recorder— The  Mallet  Perforator— Adjust- 
ment of  the  Perforator — Key-board  Perforators — The  Automatic  Transmitter — 
The  Motive  Power  of  the  Transmitter — Transmitter  Connections — The  Postal 
Automatic — The  Re-perforator — The  Reproducer — The  Tape  Moving  Mechan- 
ism— Names  of  Printing  Telegraph  Systems  Tried  Out  and  in  Service. 

CHAPTER  XXI 

TELEGRAPH  AND  TELEPHONE  CIRCUITS  AS    AFFECTED   BY    ALTERNATING-CURRENT 
LINES. — TRANSPOSITION  OF  WIRES  USED  FOR  TELEPHONE  PURPOSES,  AND  FOR 

SIMULTANEOUS  TELEPHONE  AND  TELEGRAPH  PURPOSES 424 

Presence  of  Electrostatic  and  Electromagnetic  Fields  in  the  Space  Surrounding 
Charged  Conductors — Circuit  Arrangements  for  Neutralizing  Induction — Screen- 
ing Morse  Relays  in  Grounded  Circuits  from  the  Effects  of  Induction  from 
Neighboring  High- tension  Lines — Protective  System  for  Polar  Duplex  Circuits — 
Transposition  of  Wires  on  Pole  Lines. 


xvi  CONTENTS 

CHAPTER   XXII 

PAGE 

TELEPHONY — SIMULTANEOUS  TELEGRAPHY  AND  TELEPHONY  OVER  THE  SAME  WIRES  .  432 
The  Grounded  Line  Telephone  Circuit — Metallic  Telephone  Circuits — Series 
Telephone  Set — Bridging  Telephone  Set — Batteries  used  in  Telephone  Trans- 
mitter Circuits — Connecting  Grounded  Lines  to  Metallic  Circuits — Utilizing  a 
Section  of  a  Through  Telegraph  Wire  to  Form  One  Side  of  a  Telephone  Circuit  for 
Short  Distances — Retardation  coils — Formula  for  determining  Impedance  of  Re- 
tardation Coils — The  Simplex  Circuit — Repeating  Coil,  and  Bridged  Impedance 
Types  of  Simplex — Relative  Transmission  Efficiency  of  Various  Gages  and  Kinds 
of  Wire — Simplex  Circuits  with  Intermediate  Telephone  Stations — Simplex  Cir- 
cuits with  Intermediate  Telegraph  and  Intermediate  Telephone  Stations  Inserted — 
Phantom  Telephone  Circuits — Special  Forms  of  Line  Transposition  Required 
with  Phantom  Circuits — Inserting  Intermediate  Stations  in  the  Physical  Circuits 
and  in  the  Phantom  Circuits — The  Phantom  Simplex  Circuit — Composite  Tele- 
graph and  Telephone  Circuits — The  Grounded  Line  Composite — Howler  Signaling 
— Metallic  Circuit  Composite — Repeating  Coils  and  Retardation  Coils  used  in 
Simplex  and  Composite  Circuits. 

CHAPTER  XXIII 

SPECIFICATIONS  FOR  COPPER  AND  IRON  WIRE,  AERIAL,  UNDERGROUND,  SUBMARINE, 

AND  OFFICE  CABLES .   , ......   449 

Hard-drawn  Copper  Line  Wire — Galvanized  Iron  Wire — Stranded  Galvanized 
Steel  Wire — Aerial  Twisted  Pair  (rubber  compound  dielectric)  Cable — Lead- 
covered  Aerial  or  Underground  Saturated  Paper  Cable — Lead-covered  twisted  pair 
Paper  Submarine  Cable — Lead-covered  Twisted  Pair  Paper  Cable — Aerial  (rubber 
compound  dielectric)  Cable— Office  Cable— Office  Wires— Table  of  Standard 
Rubber  Compound  Insulated  Wires. 

CHAPTER   XXIV 

ELECTROLYSIS  OF  UNDERGROUND  CABLE  SHEATHS 467 

Electrolytic  Action  between  Underground  Cable  Sheaths  and  Track  Rails  of 
Trolley  Railroad  Systems — Method  of  Determining  where  Electrolysis  is  Liable 
to  Occur — Use  of  the  Low  Reading  Voltmeter  in  Locating  Stray  Currents  in 
Underground  Cable  Sheaths — Bonding  Cables — Cable  to  Cable,  and  Cable  to 
Rail  Bonding. 

APPENDIX  A 471 

References  to  Printing  Telegraph  Literature. 

APPENDIX  B 473 

Specifications  for  the  Construction  of  High-tension  Transmission  Lines  above 
Telegraph  Wires — Constants,  Unit  Stresses  and  Formulae  to  be  used  in  Computing 
Strength  of  Transmission  Lines. 

APPENDIX  C 492 

Telegraph  Alphabets. 

APPENDIX  D 493 

Useful  Tables — Coil  Windings,  Resistance,  and  Operating  Currents  of  Telegraph 
Instruments — Wire  Gages — Current  Required  to  Fuse  Wires  of  Copper,  Ge  rman 
Silver  and  Iron — Thermometer  Scales. 

INDEX 499 


AMERICAN  TELEGRAPH  PRACTICE 

CHAPTER  I 

ELECTRICITY  AND  MAGNETISM 
UNITS  AND  SYMBOLS 

Electrical  action  for  practical  purposes  may  be  developed  in  several  different 
ways.  While  electricity  is  the  same,  no  matter  what  means  are  employed  for 
its  production,  for  the  purpose  of  distinguishing  between  one  means  and  another 
it  is  "customary  to  refer  to  it  under  different  classifications,  such  as  Frictipnal 
Electricity,  Thermal  Electricity,  Chemical  Electricity,  Magneto-electricity,  etc. 

Friction  between  a  glass  rod  and  a  piece  of  silk  produces  a  positive  charge 
upon  the  surface  of  the  glass,  while  the  charge  developed  upon  resinous  bodies 
by  friction  with  a  piece  of  dry  fur  or  flannel  is  negative.  In  each  case  an  equal 
quantity  of  both  charges  is  produced;  that  is,  in  the  case  of  the  glass  and 
silk,  the  glass  assumes  a  positive  charge  and  the  silk  assumes  a  negative 
charge  of  equal  quantity.  In  other  words,  one  charge  appears  upon  the  body 
rubbed  and  an  equal  amount  of  the  opposite  charge  appears  upon  the  "rubber." 
The  amount  or  quantity  of  charge  developed  upon  either  body  is  independent 
of  the  duration  of  friction,  provided  the  entire  surface  of  each  body  is  brought 
into  intimate  contact  with  that  of  the  other  body.  Further  investigation  along 
this  line  would  show  that  electrified  bodies  bearing  similar  charges  are  mutually 
repellant,  while  electrified  bodies  bearing  dissimilar  charges  are  mutually 
attractive. 

The  Electrophorus,  the  Toepler-Holtz,  and  the  Wimshurst  machines  are 
well-known  generators,  so  called,  of  frictional  electricity. 

Thermal. — Thermal  methods  of  producing  electrical  manifestations  have 
nothing  to  do  with  practical  telegraphy  and  shall  not  be  considered  here. 

Chemical. — Chemical  electricity  has  to  do  with  the  various  forms  of  chem- 
ical batteries  used  in  telegraphy  for  the  purpose  of  producing  the  effect  referred 
to  as  electric  current. 

Magneto-  or  Dynamo-electricity. — Magneto-electricity  or  dynamo-electri- 
city is  that  derived  by  revolving  by  mechanical  power,  coils  of  insulated  wire 
within  the  sphere  of  influence  of  magnets. 

MAGNETISM 

The  natural  magnet,  or  lodestone,  is  known  as  magnetite  and  has  a  chemical 
composition  FeaO^  This  substance  is  found  in  various  parts  of  Europe  and  in 
the  United  States.  Its  usual  form  is  octahedron,  although  some  fairly  well- 
developed  crystal  specimens  have  been  found. 

1 


AMERICAN  TELEGRAPH  PRACTICE 


If  a  piece  of  hard  iron  or  steel  be  rubbed  with  a  piece  of  Iqdestone,  it  will 
be  found  to  have  taken  on  magnetic  properties. 

A  magnet  sets  up  in  the  space  immediately  surrounding  it  a  disturbance 
referred  to  as  a  magnetic  field — a  region  pervaded  by  invisible  lines  of  force. 
These  lines  act  upon  neighboring  pieces  of  iron,  iron  filings,  or  other  magnetic 
substances  by  what  is  commonly  called  magnetic  induction.  A  magnet  which 
retains  its  magnetism  indefinitely  and  independently  is  called  a  permanent 
magnet,  familiar  forms  of  which  are  the  bar  magnet  and  the  horseshoe  magnet. 
If  a  magnet  be  suspended  by  means  of  a  thread  or  fiber  and  is  free  to  turn 
in  any  direction,  the  presence  of  another  magnet  in  close  proximity  to  it  will 
cause  the  first  to  set  itself  in  a  definite  position  relatively  to  the  second  magnet, 
and  the  imaginary  line  joining  the  poles  of  these  magnets  is  called  the  magnetic 
axis.  The  greatest  manifestation  of  magnetic  force  exerted  by  a  magnet  occurs 
at  .its  ends  or  poles,  and  the  two  poles  of  a  given  magnet  exhibit  opposite  char- 
acteristics which  in  practice  are  designated  north  and  south,  for  reasons  to 
be  explained  later. 

Substances  which  are  attracted  by  magnets  when  either  pole  is  presented 
to  them  are  called  magnetic  substances.  Most  common  among  such  sub- 
stances are  iron,  steel,  nickel,  cobalt,  chromium  and  manganese.  Such  sub- 
stances are  paramagnetic. 

If  a  piece  of  soft  iron  be  magnetized  by  means  of  a  permanent  magnet  it 
will  lose  practically  all  of  its  magnetic  properties  upon  the  withdrawal  of  the 
exciting  magnet;  any  trace  of  magnetism  which  remains  is  termed  residual  mag- 
netism. To  magnetize  a  piece  of  steel  requires  longer  time,  but  it  is  found  that 
steel  retains  its  magnetic  properties  a  much  greater  length  of  time  than  does 
soft  iron.  One  peculiarity  of  magnets  is  that  their  magnetism  is  materially 
impaired  if  they  are  subjected  to  knocks  or  jars. 

RELATION  BETWEEN  ELECTRICITY  AND  MAGNETISM 

The  discovery  was  made  in  the  year  1820  that  a  wire  conveying  an  electric 
current  exhibits  characteristics  practically  identical  with  those  peculiar  to 
magnets.  That  is,  it  was  found  that  the  space  immediately  surrounding  the 
wire  is  charged  magnetically  and  so  affects  a  magnetic  needle  that  the  latter 
tends  to  take  up  a  position  at  right  angles  to  the  conducting  wire.  This  dis- 
covery very  quickly  led  to  the  development  of  electromagnets,  now  so  ex- 
tensively employed  in  nearly  all  methods  of  electric  telegraphy. 

CONDUCTORS  AND  INSULATORS 

Conductors. — Conductors  of  electricity,  so  called,  consist  of  substances 
which  freely  permit  electrical  action  to  progress  from  one  portion  of  their  mass 
to  another.  Insulators,  or  non-conductors,  are  substances  which  do  not 
permit  of  unhampered  progress  of  electrical  action  through  them.  The  terms 


ELECTRICITY  AND  MAGNETISM  3 

conductor  and  insulator  are  relative  distinctions,  however,  as  it  is  well  known 
that  the  best  conductor  available  is  far  from  being  a  perfect  medium  for  the 
free  progress  of  electrical  action,  and  on  the  other  hand  it  can  be  shown  that 
the  best  insulator  available  is  in  a  sense  a  conductor,  as  it  is  unable  to  completely 
stop  the  passage  of  the  electric  current.  The  best  conductors  are  metals  in  the 
following  order  of  conductivity: 

Silver  Iron 

Copper  Tin 

Gold  Lead 

Zinc  Mercury 
Platinum 

Next  in  order  of  conductivity  comes  carbon,  the  acids,  saline  solutions,  and 
water. 
Insulators. — Insulators  taken  in  order  of  their -insulating  qualities  are: 

Dry  air  Silk 

Glass  Wool 

Ebonite  Porcelain 

Paraffine  Oils 

India  rubber  Paper 

Gutta  percha  Marble 

Potential  Energy. — Mechanical  energy  is  recognized  in  two  forms:  kinetic 
energy  and  potential  energy. 

When  a  body  moves,  it  moves  as  a  result  of  pressure  having  been  exerted 
upon  it  by  another  body;  the  moving  body  then  possesses  kinetic  energy — the 
energy  of  motion. 

Potential  energy  may  exist  without  producing  motion,  as  in  the  case  of  a 
coiled  steel  spring  or  a  suspended  weight.  One  may,  for  instance,  attempt 
to  move  a  stone  building  by  placing  his  shoulder  against  it,  but  there  is  no 
movement  of  the  body  acted  upon,  in  which  case  there  exists  potential  energy 
without  any  resultant  kinetic  energy. 

Because  of  the  similarity  between  the  action. of  electricity  in  metallic  con- 
ductors, and  the  flow  of  water  in  pipes,  the  hydraulic  analogy  has  for  many 
years  been  employed  for  the  purpose  of  dealing  with  something  tangible  while 
explaining  the  behavior  of  electricity  in  conducting  wires.  The  principles 
of  hydraulics  do  not  conflict  with  practical  conceptions  of  electrical  action 
based  on  the  electron  theory,  for,  when  one  understands  that  the  universe  is 
as  full  of  what  we  term  electricity  as  the  ocean  bed  is  of  water,  the  use  of  the 
hydraulic  analogy  may  be  extended  to  meet  modern  requirements. 

We  know  that  water  from  the  ocean  is  lifted  up  by  evaporation  and  deposited 
in  the  hills  in  the  form  of  snow  and  rain,  thereafter  to  be  conducted  from  a 
higher  level  back  to  the  level  of  the  sea  by  way  of  conducting  channels  which 
we  call  rivers.  During  its  transfer  from  a  higher  to  a  lower  level  the  energy 


4  AMERICAN  TELEGRAPH  PRACTICE 

of  the  falling  water  may  be  availed  of  to  turn  water  wheels  and  furnish  power. 
Similarly,  when  the  equilibrium  of  the  electricity  of  the  universe  is  disturbed 
by  any  one  of  the  various  means  employed  to  set  it  in  motion,  the  potential 
energy  thus  created  may  be  availed  of  during  the  process  of  readjustment  by 
presenting  a  convenient  channel  through  which  equilibrium  may  be  restored. 
In  practical  operations  the  channel  provided  is  known  as  an  electric  circuit. 

Electric  Potential.  —  Electric  potential,  or  difference  of  potential  is  a 
difference  of  electric  condition  between  two  separated  points  along  a  con- 
ductor, or  between  two  bodies,  by  virtue  of  which  work  is  done  as  a  result  of 
the  progress  of  electrical  action  from  one  point  to  the  other,  or  from  one  body 
to  the  other  as  the  case  may  be. 

The  electric  potential  of  a  body  or  a  point  refers  to  the  potential  of  the  body 
or  the  point  as  compared  with  the  potential  of  the  earth,  which  is  assumed  to 
be  nil. 

The  property  of  producing  a  difference  of  electric  potential  is  regarded  as 
being  due  to  a  force  referred  to  as  electromotive  force. 

When  it  is  stated  that  a  certain  battery  or  dynamo  produces  a  definite 
electromotive  force,  it  is  meant  that  a  certain  definite  difference  of  potential 
is  thereby  created  between  the  terminals  of  the  battery  or  the  dynamo. 

It  is  to  be  specially  noted  that  electromotive  force  is  not  a  mechanical  force 
capable  of  setting  a  mass  in  motion,  but  rather  a  name  given  to  the  supposed 
force  which  causes  a  transfer  of  electrical  action  from  one  point  to  another  in 
an  electrical  conductor. 

An  electromotive  force  may  exist  without  producing  electric  current,  in  the 
same  sense  that  mechanical  potential  energy  may  exist  without  producing 
kinetic  energy. 

The  unit  in  which  electromotive  force  is  measured  is  the  volt. 

Resistance. — Resistance  refers  to  that  quality  of  a  conductor  by  virtue  of 
which  it  opposes  the  free  flow  of  electricity. 

The  value  of  the  resistance  in  ohms  of  a  conductor  depends  upon  the  physical 
dimensions,  temperature,  and  the  kind  of  material  of  which  the  conductor  is- 
composed. 

The  resistance  of  a  continuous  wire  of  constant  section  and  material  is 
directly  proportional  to  the  length  and  inversely  proportional  to  its  cross-section. 

The  resistance  of  telegraph  circuits,  made  up  as  they  are  through  circuit- 
controlling  contact  points,  consists  of  the  resistance  of  the  conductor  and  the 
resistance  due  to  imperfect  contacts. 

The  unit  of  resistance  is  the  ohm. 

Current. — A  current  of  electricity  is  said  to  flow  when  two  points  in  a  con- 
ductor are  at  a  difference  of  potential,  in  a  manner  analogous  to  the  flow  of 
water  from  a  high  to  a  lower  level  when  a  conduit  or  channel  is  provided  for 
it;  obviously  a  flow  can  take  place  only  when  a  path  is  opened  for  the  transfer. 
Hence/ to  have  a  current  of  electricity  all  that  is  required  is  an  applied  electro- 


UNITS  AND  SYMBOLS  5 

motive  force  and  a  closed  conducting  circuit  joining  the  terminals  of  the  source 
of  e.m.f .  Of  course,  as  is  brought  out  in  a  later  chapter,  a  current  may  be  in- 
duced in  a  circuit  without  direct  application  of  an  electromotive  force;  and  it 
is  true,  also,  that  a  current  of  electricity  can  be  present  in  a  circuit  made  up 
of  earth,  water,  and  of  any  conducting  substance  which  may  be  so  arranged 
that  a  continuous  path  is  provided  for  it  from  a  point  of  higher  to  a  point  of 
lower  potential.  But  the  strength  of  current  present  in  any  circuit  varies 
directly  as  the  electromotive  force,  and  inversely  as  the  resistance.  The 
practical  unit  of  current  is  the  ampere. 

UNITS  AND  SYMBOLS 

A  unit  is  the  base  of  a  system  of  measurement. 

The  statement  of  Ohm's  law  given  in  the  latter  part  of  the  paragraph  on 
Current,  might  be  paraphrased  in  the  following  words :  resistance  equals  electro- 
motive force  divided  by  current;  electromotive  force  equals  current  multiplied 
by  resistance,  and  current  equals  electromotive  force  divided  by  resistance. 

It  is  evident,  then,  from  the  above  that  when  any  two  of  these  factors  are 
known  the  third  may  readily  be  calculated. 

It  is  to  be  remembered,  however,  that : 

resistance  is  stated  in  ohms, 
e.m.f.  is  stated  in  volts,  and 
current  is  stated  in  amperes. 

The  symbols  given  herewith  are  those  commonly  employed  in  electrical  calcu- 
lations and  while  some  of  those  listed  are  not  encountered  in  everyday  work  it 
is  desirable  and  convenient  to  list  them  all  in  one  place. 
Fundamental  Units. 

I,  Length,  centimeter. 

M,  Mass,  gram. 

T,  t,  Time,  seconds. 

"*     Derived,  mechanical. 

d,  Dyne. 

e,  Ergs. 

Ft.  Ib.j  Foot-pounds. 

h.p.  Horse-power. 

J  Joules'  equivalent. 
Derived,  electrostatic. 

q,  Quantity. 

i,  Current. 

e,  Potential  difference. 

r,  Resistance. 

k,  Capacity. 

sk,  Specific  inductive  capacity. 


AMERICAN  TELEGRAPH  PRACTICE 

Derived,  magnetic. 

m,  Strength  of  pole. 

*srlt  Magnetic  moment. 

«^  Intensity  of  magnetization. 

3(t  Horizontal  intensity  of  earth's  magnetism. 

5H,  Field  intensity. 

$,  Magnetic  flux. 

38,  Magnetic  flux  density,  or  magnetic  induction. 

J{,  Magnetizing  force. 

&,  Magnetomotive  force. 

t%  Reluctance,  magnetic  resistance. 

ft,  Magnetic  permeability. 

K,  Magnetic  susceptibility. 

v,  Reluctivity  (specific  magnetic  resistance). 

Derived,  electromagnetic. 

R,  Resistance,  ohm. 

&,  Resistance,  megohm. 

E,  Electromotive  force,  volt. 

U,  Difference  of  potential,  volt. 

/,  Intensity  of  current,  ampere. 

Q,  Quantity  of  electricity,  ampere-hour;  coulomb. 

C,  Capacity,  farad. 

W,  Electric  energy,  watt-hour;  joule. 

P,  Electric  power,  watt,  kilowatt. 

p,  Restivity  (specific  resistance),  ohm-centimeter. 

G,  Conductance,  mho. 

Y,  Conductivity  (specific  conductivity). 

Y,  Admittance,'  mho. 

Z,  Impedance,  ohm. 

X,  ,   Reactance,  ohm. 

B,  Susceptance,  mho. 

L,  Inductance  (coefficient  of  induction),  henry. 

Miscellaneous  Symbols  in  General  Use. 

D,  Diameter. 
r,  Radius. 

#,  Deflection  of  galvanometer  needle. 

TT,  Circumference  divided  by  diameter  =  3.141592 

LO,  Frequency,  periodicity,  cycles  per  second. 

B.  &  S.  Brown  &  Sharpe  wire  gage. 

B.  W.  G.  Birmingham  wire  gage. 

Seconds,  or  inches. 

Minutes,  or  feet. 


UNITS  AND  SYMBOLS  7 

+  Positive,  or  plus. 

Negative,  or  minus. 

Electrical  units  are  expressed  in  terms  of  the  centimeter,  gram,  second  or 
c.g.s.  system. 

The  centimeter  is  equal  to  0.3937  m- 

The  gram  is  equal  to  15.432  grains. 

The  second  is  the  1/86400  part  of  a  mean  solar  day. 

These  units  are  generally  referred  to  as  the  fundamental  or  absolute  units. 
From  these  the  derived  or  practical  units  of  measurement  have  been  deter- 
mined, in  order  that  the  requirements  of  common  practice  may  be  met  with 
standards  which  are  immediately  available. 

.  The  unit  of  force  is  that  force  which,  acting  for  i  second  on  a  mass  of  i  grm., 
gives  the  mass  a  velocity  of  i  cm.  per  second.     The  unit  is  the  dyne. 

Work. — Work  is  the  product  of  a  force  into  the  distance  through  which  it 
acts.  The  unit  is  the  erg,  and  equals  the  work  done  in  pushing  a  mass  through 
a  distance  of  i  cm.  against  a  force  of  i  dyne. 

Power. — Power  is  the  rate  of  working,  and  the  unit  is  the  watt  =  io7  ergs 
per  second. 

Horse-power. — Horse-power  is  the  unit  of  power  in  common  use  and  is 
equivalent  to  raising  33,000  Ib.  i  ft.  in  i  minute,  or  550  ft.-lb.  per  second. 

i  watt  =  io7  ergs  per  second.  . 

i  horse-power  =  550X1. 356Xio7  ergs  =  746  watts. 

The  Joule. — The  joule  (WJ)  =  io7  ergs,  and  is  the  work  done,  or  heat 
generated,  by  a  watt-second;  or  i  ampere  flowing  for  i  second  through  a 
resistance  of  i  ohm. 

The  Calorie. — The  calorie  is  the  amount  of  heat  required  to  raise  the 
temperature  of  i  grm.  of  water  i°  C. 

Joules  equivalent,  /,  is  the  amount  of  energy  equal  to  a  heat  unit. 

The  electrostatic  units  derived  from  the  fundamental  c.g.s.  units  are  based 
on  the  force  exerted  between  two  quantities  of  electricity,  while  the  electro- 
magnetic units  so  derived  are  based  upon  the  force  exerted  between  a  current 
and  a  magnetic  pole. 

ELECTROSTATIC  UNITS 

So  far  no  names  have  been  assigned  to  the  electrostatic  units,  but  what  is 
called  the  unit  of  quantity  is  that  quantity  of  electricity  which  repels  with  a 
force  of  one  dyne  a  similar  and  equal  quantity  of  electricity  placed  at  unit 
distance  (i  cm.)  in  air. 

Unit  of  Current. — Unit  of  current  is  that  which  conveys  a  current  of  unit 
quantity  along  a  conductor  in  unit  time  (i  second). 

Unit  Difference  of  Potential,  or  Unit  Electromotive  Force. — Unit  difference 
of  potential,  or  electromotive  force  exists  between  two  points  when  one  erg 


8  AMERICAN  TELEGRAPH  PRACTICE 

of  work  is  required  to  pass  a  unit  quantity  of  electricity  from  one  point  to  the 
other. 

Unit  of  Resistance. — Unit  of  resistance  is  possessed  by  that  conductor 
through  which  unit  current  will  pass  under  unit  electromotive  force  at  its  ends. 

Unit  of  Capacity. — Unit  of  capacity  is  that  which,  when  charged  by  unit 
potential,  will  hold  one  unit  of  electricity;  or  that  capacity  which,  when  charged 
with  one  unit  of  electricity,  has  a  unit  difference  of  potential. 

Specific  Inductive  Capacity. — Specific  inductive  capacity  of  a  substance  is 
the  ratio  between  the  capacity  of  a  condenser  having  that  substance  as  a  dielec- 
tric to  the  capacity  of  the  same  condenser  using  dry  ah*  as  the  dielectric  at  o°  C., 
and  a  pressure  of  76  cm. 

MAGNETIC  UNITS 

Unit  Strength  of  Pole. — Unit  strength  of  pole  (symbol  m)  is  that  which 
repels  another  similar  and  equal  pole  with  unit  force  (i  dyne)  when  placed 
at  unit  distance  (i  cm.)  from  it. 

Magnetic  Moment. — Magnetic  moment  (symbol  ^M)  is  the  product  of  the 
strength  of  either  pole  into  the  distance  between  the  two  poles. 

Intensity  of  Magnetization. — In  tensity  of  magnetization  (symbol  ^7)  is  the 
magnetic  moment  of  a  magnet  divided  by  its  volume. 

Intensity  of  Magnetic  Field. — Intensity  of  the  magnetic  field  (symbol  ^¥) 
is  measured  by  the  force  the  magnetic  field  exerts  upon  a  unit  magnetic  pole, 
and  therefore  the  unit  is  that  intensity  of  field  which  acts  on  a  unit  pole  with  a 
unit  force  (i  dyne). 

Magnetic  Induction. — Magnetic  induction  (symbol  38}  is  the  magnetic  flux 
or  the  number  of  magnetic  lines  per  unit  area  of  cross-section  of  magnetized 
material,  the  area  being  at  every  point  perpendicular  to  the  direction  of  flux. 
It  is  equal  to  the  magnetizing  force  or  field  intensity  multiplied  by  the  permea- 
bility; the  unit  is  the  gauss. 

Magnetic  Flux. — Magnetic  flux  (symbol  $)  is  equal  to  the  average  field 
intensity  multiplied  by  the  area.  Its  unit  is  the  maxwell. 

Magnetizing  Force. — Magnetizing  force  (symbol  7i}  per  unit  of  length  of  a 
solenoid  equals  ^nNI  divided  by  L;  where  N  equals  the  number  of  turns  of  wire 
on  the  solenoid;  L  equals  the  length  of  the  solenoid  in  centimeters,  and  I 
equals  the  current  in  absolute  units. 

Magnetomotive  Force. — Magnetomotive  force  (symbol  ^)  is  the  total  mag- 
netizing force  developed  in  a  magnetic  circuit  by  a  coil;  the  unit  is  the  gilbert. 

Reluctance,  or  Magnetic  Resistance. — Reluctance,  or  magnetic  resistance 
(symbol  ^)  is  the  resistance  offered  to  the  magnetic  flux  by  the  material  mag- 
netized, and  is  the  ratio  of  magnetomotive  force  to  magnetic  flux,  that  is,  unit 
magnetomotive  force  will  generate  a  unit  of  magnetic  flux  through  unit  re- 
luctance; the  unit  is  the  oersted;  i.e.,  the  reluctance  offered  by  a  cubic  centi- 
meter of  vacuum. 


UNITS  AND  SYMBOLS  9 

Magnetic  Permeability. — Magnetic  permeability  (symbol  /*)  is  the  ratio 

£B 

of  the  magnetic  induction  to  the  magnetizing  force  3(t  that  is  -—,  =  /*. 

Magnetic  Susceptibility. — Magnetic  susceptibility  (symbol  K)  is  the  ratio 

£p 
of  the  intensity  of  magnetization  to  the  magnetizing  force,  or  K  —  ~^=* 

Reluctivity,  or  Specific  Magnetic  Resistance. — Reluctivity,  or  specific  mag- 
netic resistance  (symbol  u)  is  the  reluctance  per  unit  of  length  and  of  unit  cross- 
section  that  a  material  offers  to  being  magnetized. 

ELECTROMAGNETIC  UNITS 

Resistance. — Resistance  (symbol  R)  is  that  property  of  a  material  that 
opposes  the  flow  of  a  current  of  electricity  through  it;  and  the  unit  is  that  re- 
sistance which  with  an  electromotive  force  or  pressure  between  its  ends  of  i 
volt  will  permit  the  flow  of  a  current  of  i  ampere. 

The  practical  unit  of  resistance  is  the  ohm,  and  its  value  in  c.g.s.  units  is 
io9.  The  standard  unit  is  a  column  of  pure  mercury  at  a  temperature  of  o°  C., 
of  uniform  cross-section,  106.3  cm-  l°ng  and  14.4521  grm.  weight.  For  con- 
venience, when  high  resistances  are  being  measured,  such  as  the  insulation  of 
telegraph  lines  or  cables,  the  prefix  meg,  meaning  million,  is  used;  thus  is  derived 
the  megohm. 

Electromotive  Force. — Electromotive  force  (symbol  E)  is  the  electric 
pressure  which  forces  the  current  through  a  resistance.  Unit  e.m.f .  is  that 
pressure  which  will  force  a  unit  current  of  i  ampere  through  unit  re- 
sistance. The  unit  is  the  volt,  and  the  practical  standard  adopted  by  the 
London  conference  in  1908,  is  the  Weston  cell  which  has  an  e.m.f.  of  1.01830 
international  volts  at  a  temperature  of  20°  C.  The  value  of  the  volt  in  c.g.s. 
units  is  io8. 

Kilo-volt. — The  kilo-volt  =  i  ,000  volts,  and  the  milli- volt  =  i/iooovolt. 

Current. — Current  (symbol  7)  is  the  intensity  of  the  electric  current  that 
flows  through  a  circuit.  A  unit  current  will  flow  through  a  resistance  of 
i  ohm,  with  an  e.m.f.  of  i  volt  between  its  ends.  The  unit  is  the  ampere, 
and  is  practically  represented  by  the  current  that  will  deposit  silver  electro- 
lytically  at  the  rate  of  0.001118  grm.  per  second.  Its  value  in  c.g.s.  units  is 
io-1.  The  milliampere  is  i/iooo  ampere. 

Quantity  of  Electricity. — The  quantity  of  electricity  (symbol  Q)  which 
passes  through  a  given  cross-section  of  an  individual  circuit  in  t  seconds  when 
a  current  of  7  amperes  is  flowing  is  equal  to  (It)  units.  The  unit  is  therefore  the 
ampere-second.  Its  name  is  the  coulomb,  and  its  value  in  c.g.s.  units  is  lo"1. 

Capacity. — Capacity  (symbol  C)  is  the  property  of  a  material  condenser  for 
holding  a  charge  of  electricity.  A  condenser  of  unit  capacity  is  one  which  will 
be  charged  to  a  potential  of  i  volt  by  a  quantity  of  i  coulomb.  The  unit  is  the 
farad.  Its  c.g.s.  value  is  io~9,  and  this  being  so  much  larger  than  ever  obtains 


10  AMERICAN  TELEGRAPH  PRACTICE 

in  practical  work,  its  millionth  part,  or  the  microfarad,  is  used  as  the  practical 
unit,  and  its  value  in  absolute  units  is  io~15.  Condensers  used  in  telegraphy 
are  usually  made  adjustable  from  i/io  mfd.  to  3  mfd. 

Electric  Energy. — Electric  energy  (symbol  W)  is  represented  by  the  work 
done  in  a  circuit  or  conductor  by  a  current  flowing  through  it.  The  unit  is 
the  joule,  its  absolute  value  is  io7  ergs,  and  it  represents  the  work  done  by  the 
flow  for  i  second  of  unit  current  (i  ampere)  through  i  ohm. 

Electric  Power. — Electric  power  (symbol  P)  is  measured  in  watts  and  is 
represented  by  a  current  of  i  ampere  under  a  pressure  of  i  volt  or  i  joule 
per  second.  The  watt  =  io7  absolute  units,  and  746  watts  =  i  h.p.  In  electric 
lighting  and  power  operations  the  unit  kilowatt  (1,000  watts)  is  generally 
employed  to  avoid  the  use  of  large  numbers. 

Resistivity. — Resistivity  (symbol  p)  is  the  specific  resistance  of  a  substance, 
and  is  the  resistance  in  ohms  of  a  centimeter  cube  of  the  material  to  a  flow  of 
current  between  opposite  faces. 

Conductance. — Conductance  (symbol  G)  is  the  property  of  a  metal  or 
substance  by  which  it  conducts  an  electric  current,  and  equals  the  reciprocal 
of  its  resistance.  The  unit  proposed  for  conductance  is  the  mho,  but  it  has  not 
come  into  extensive  use  as  yet. 

Conductivity. — Conductivity  (symbol  If)  is  the  specific  conductance  of  a 
material,  and  is  therefore  the  reciprocal  of  its  resistivity.  It  is  often  expressed 
in  comparison  with  the  conductivity  of  some  metal  such  as  silver  or  copper 
and  is  then  stated  as  a  percentage. 

Inductance. — Inductance  (symbol  L)  or  coefficient  of  self-inductance  of 
a  current  is  that  coefficient  by  which  the  time  rate  of  change  of  the  current  in 
the  circuit  must  be  multiplied  in  order  to  give  the  e.m.f.  of  self-induction  in 
the  circuit.  The  practical  unit  is  the  henry,  which  equals  io9  absolute  units, 
and  exists  in  a  circuit  when  a  current  varying  i  ampere  per  second  produces  a 
volt  of  electromotive  force  in  that  circuit.  The  millihenry  is  equal  to  i/iooo 
henry. 

In  the  operation  of  telegraph  lines  the  factor  of  inductance  in  open  air  lines 
is  almost  negligible,  but  the  inductance  of  signaling  instruments  employed 
in  terminal  equipment  is  of  considerable  consequence;  indeed  in  some  cases 
the  receiving  end  inductance  is  a  criterion  of  speed. 

Practical  methods  of  testing  the  inductance  of  coils  and  magnets  will  be 
taken  up  later. 


CHAPTER  II 
PRIMARY  BATTERIES 

Although  at  the  present  time  dynamo  machinery  is  employed  to  furnish 
most  of  the  electric  current  used  in  telegraph  operation,  the  fact  that  nearly 
half  a  million  dollars  are  paid  annualy  for  gravity-battery  materials  would 
indicate  that  primary  batteries  are  still  used  extensively  as  sources  of  power. 

It  must  be  admitted  that  the  primary  batteries  in  use  to-day  are  practically 
the  same  in  design  and  construction  as  those  employed  in  the  operation  of  the 
early  telegraph  systems.  Little  or  no  advance  in  this  regard  has  been  made. 
Certain  objections  to  their  use,  probably  considered  inherent,  have  never 
been  satisfactorily  overcome.  The  objectionable  features  are:  high  internal 
resistance,  loose  and  easily  deranged  assembly  of  elements,  poorly  designed 
terminal  connections,  high  cost  of  supervision,  and  high  cost  of  constituent 
materials. 

The  function  of  a  battery  is  to  maintain  in  a  conducting  circuit,  an  electric 
current  by  means  of  chemical  action  set  up  between  two  dissimilar  metals 
conveniently  immersed  in  an  electrolyte  which  possesses  a  chemical  affinity 
for  one  of  these  metals.  The  activity  of  this  action  in  a  given  type  of  cell 
determines  the  voltage  or  electromotive  force  of  the  battery.  The  voltage  of 
a  cell  is  in  great  part  dependent  upon  the  particular  metals  and  electrolytes 
employed  in  its  assembly.  One  of  the  elements  is  termed  the  anode  and  the 
other  the  cathode.  In  the  gravity  cell,  for  instance,  the  zinc  is  the  anode  and 
the  copper  the  cathode.  In  each  case  the  former  is  the  positive  plate  and  the 
latter  the  negative  plate.  The  atoms  which  gather  at  each  plate  are  called 
anions  and  cathions  respectively. 

For  telegraph  working  it  is  necessary  to  have  a  type  of  battery  which  will 
not  quickly  lose  its  strength  on  closed  circuit.  Sounder  circuits  and  main-line 
circuits  are  frequently  closed  several  minutes  and  sometimes  for  hours  at  a 
time,  so  that  a  battery,  such  as  the  well-known  dry-cell,  which  "runs  down" 
quickly  when  short  circuited  or  when  connected  in  circuits  having  low  re- 
sistances, would  not  be  suitable  for  closed-circuit  telegraph  work. 

Batteries,  then,  are  classified  as  open-circuit  types  or  closed-circuit  types. 
TheLeClanche  and  the  dry-cell  are  examples  of  the  former,  while  the  gravity, 
Edison-Lalande  and  the  Fuller  cells  are  examples  of  the  latter.  Again, 
battery  cells  are  classified  as  single-fluid  or  double-fluid  types.  TheLe- 
Clanche and  Lalande  are  single-fluid  cells  while  the  gravity  and  Fuller  are 
double-fluid  cells. 

11 


12 


AMERICAN  TELEGRAPH  PRACTICE 


Before  going  into  a  detailed  description  of  the  action  and  construction  of 
the  various  types  of  battery  used  in  practice  it  may  be  well  for  the  purpose 
of  reference  to  give  some  tabulated  data  in  regard  to  the  general  subject. 

CHEMICALS  COMMONLY  EMPLOYED  AND  THEIR  SYMBOLS 

Symbol 

Hydrogen H 

Potassium K 

Copper  (cupric) Cu 

Carbon C 

Platinum Pt 

Ammonium  chloride  (Sal-ammoniac) NH4C1 

Bichromate  of  potassium K2Cr2O7 

Bichromate  of  soda Na2Cr2O7 

Cadmium  sulphate CdSO4 

Chromic  acid CrOs 

Copper  oxide CuO 

Caustic  potash  or  potassium  hydrate KOH 

Copper  sulphate  (blue- vitriol) CuSO4 

Hydrochloric  acid HC1 

Lead  oxide PbO 

Lead  peroxide PbO2 

Mercurous  sulphate Hg3SO4 

Manganese  dioxide MnO 

Nitric  acid HNO3 

Sulphuric  acid H2SO4 

Silver  chloride. AgCl 

Sodium  chloride NaCl 

Zinc  chloride ZnCl2 

Zinc  sulphate ZnSO4 

Zinc  sulphate  (white-vitriol) ZnSO4 

TYPES  OF  CELL 

Negative    Positive  ,     .  E.M.F.     Internal 

Name  pole  pole  Electrolyte  Depolarizer 

Gravity Zinc Copper....   Zinc  sulphate Copper     sulphate        i .  07      2.5  ohms 

solution. 
LeClanche Zinc Carbon...    Ammonium  chloride.   Manganese        di-       0.75       1.5  ohm 

oxide. 
Fuller Zinc Carbon...    Sulphuric  acid Bichromate        of       2  0.5  ohm 

potassium. 
Edison-Lalande  Zinc. .  t. .    Copper....   Caustic  potash Cupric  oxide 0.8        0.050  ohm 


The  Voltaic  Cell. — A  simple  voltaic  cell  may  be  assembled  as  shown  in 
Fig.  i,  which  represents  a  zinc  and  a  copper  plate  immersed  in  a  sulphuric 
acid  solution  which  is  contained  in  a  glass  jar.  If  the  exposed  terminals  of 
the  copper  and  zinc  plates  are  joined  by  a  connecting  wire,  the  acid  attacks 
the  zinc,  the  latter  being  gradually  dissolved  forms  hydrogen  gas  which  escapes 
in  minute  bubbles.  The  chemical  action  thus  set  up  results  in  a  continuous 


PRIMARY  BATTERIES 


13 


current  from  the  zinc  (positive)  plate  to  the  copper  (negative)  plate  through 
the  liquid  (electrolyte).  The  chemical  transfer  going  on  carries  hydrogen 
bubbles  to  the  surface  of  the  copper  electrode;  from  there  the  path  or  circuit 
is  metallic — that  is,  through  the  connecting  wire  back  to  the  zinc  terminal. 

It  may  here  be  observed  that,  within  the  battery  jar  the  current  is  from 
zinc  (positive)  to  copper  (negative)  and  in  the  external  connecting  circuit  the 
current  is  from  copper  to  zinc. 

Inasmuch  as  the  function  of  the  cathode  or  negative  element  is,  mainly, 
to  serve  as  a  conductor  of  the  current  from  the  electrolyte,  although  some- 
what paradoxical,  it  is  customary  to  refer 
to  the  cathode  as  the  positive  terminal  of 
the  cell.  When  the  external  circuit  is 
closed  or  "completed"  an  electric  current 
flows  and  the  zinc  is  wasted  away.  The 
consumption  of  the  zinc  plate  furnishes  the 
energy  which  causes  the  current  to  flow 
through  the  electrolyte  and  the  connecting 
circuit.  The  cell  might  be  likened  to  a 
chemical  furnace  in  which  the  zinc  is  the 
fuel. 

The  exact  nature  of  the  chemical  action 
which  takes  place  within  the  voltaic  cell 
might  be  described  as  follows :  The  affinity 
of  the  acid  for  the  positive  plate  (zinc)  pro- 
duces a  difference  of  potential  between  the 
two  terminals  of  the  cell.  In  the  simple 
cell  employing  sulphuric  acid  as  the  elec- 
trolyte ;  we  have  first  to  consider  the  consti- 
tution of  the  acid.  Sulphuric  acid,  H2SO4, 


FIG.  1. — Simple  voltaic  cell. 


consists  of  a  group  of  atoms,  2  of  hydrogen,  i  of  sulphur,  and  4  of  oxygen. 
The  oxygen  and  sulphur  conbination  has  a  decided  affinity  for  the  zinc,  and 
when  the  copper  and  zinc  plates  are  joined  by  a  connecting  wire,  attacks  the 
zinc  plate  forming  zinc  sulphate,  ZnSO4,  which  is  dissolved  in  the  water. 
There  are,  then,  two  parts  of  hydrogen  gas  set  free  for  every  portion  of  the  SC>4 
part  of  the  sulphuric  acid  which  unites  with  the  zinc.  Thus  when  the  hydrogen 
is  liberated  the  zinc  takes  its  place.  Zinc  sulphate  and  hydrogen  are  pro- 
duced by  sulphuric  acid  and  zinc.  The  equation  representing  the  action 
which  takes  place  is  expressed  in  the  following  manner: 


Action  continues  only  as  long  as  the  external  circuit  is  closed,  that  is,  when 
the  positive  element  employed  consists  of  chemically  pure  zinc.  When,  how- 
ever, commercial  zinc  is  used,  which  in  many  instances  contains  impurities 


14  AMERICAN  TELEGRAPH  PRACTICE 

such  as  carbon,  tin,  arsenic,  lead,  iron,  etc.,  there  is  a  local  action  going  on  which 
results  in  the  consumption  of  zinc  without  the  desired  production  of  useful 
current.  For  the  purpose  of  overcoming  this  local  action  it  is  customary  to 
amalgamate  the  zinc  elements  used  in  chemical  batteries.  The  process  of 
amalgamation  consists  of  cleaning  the  surface  of  the  zinc  by  immersing  it  in 
an  acid  and  then  rubbing  upon  the  zinc  a  coating  of  mercury  which  unites 
with  the  zinc  and  forms  an  amalgam  paste.  The  foreign  matter  contained  in 
the  zinc  does  not  dissolve  in  the  mercury  but  floats  to  the  surface  and  is  carried 
off  by  the  constantly  forming  hydrogen  bubbles.  The  zinc  associated  with 
the  mercury  dissolves  in  the  acid  solution  and  the  mercury  coating  con- 
tinually uniting  with  fresh  portions  of  zinc  results  in  a  clean  bright  surface 
of  zinc  being  at  all  times  presented  to  the  attacking  acid. 

As  before  stated,  the  hydrogen  set  free  is  carried  away  in  the  form  of 
minute  bubbles,  and  while  most  of  these  bubbles  reach  the  surface  of  the 
liquid  there  releasing  their  charge,  an  increasing  number  of  them  gather  upon 
the  surface  of  the  copper  electrode,  the  longer  the  cell  is  used.  Now,  as  these 
hydrogen  bubbles  are  electropositive  in  practically  the  same  sense  as  is  the  zinc 
element  itself,  the  copper  element  by  virtue  of  this  accumulation  of  hydrogen 
bubbles  upon  its  surface,  is  converted  into  a  positive  element,  at  least  that 
would  be  the  result  if  the  action  were  permitted  to  continue  indefinitely.  This 
action  is  called  Polarization. 

There  are  several  well-known  ways  of  overcoming  this  tendency  to  polarize. 
Theoretically,  the  desired  end  might  be  accomplished  simply  by  brushing  the 
bubbles  off  the  cathode,  but  in  practice  it  is  desirable  to  secure  the  same  result 
automatically. 

It  is  customary  to  employ  as  a  constituent  of  the  cell  a  substance  with 
which  the  hydrogen  gas  will  readily  combine.  Such  substances  are  called 
Depolarizers.  Depolarizers  may  be  either  solid  or  liquid.  When  solid,  the 
usual  method  is  to  shield  the  cathode  with  a  substance  in  porous  form  as  in  the 
Leclanche  and  Fuller  types.  When  a  liquid  depolarizer  is  used,  if  its  specific 
gravity  be  less  than  that  of  the  electrolyte,  they  will  be  kept  separate  by  plac- 
ing the  lighter  on  top  of  the  heavier  liquid  as  in  the  gravity  cell. 

There  are  several  depolarizers  which  may  be  used  with  good  results,  namely, 
oxide  of  copper,  peroxide  of  manganese,  nitric  acid,  permanganate  of  potash, 
chromic  acid,  bromin  in  caustic  soda,  and  sulphate  of  copper  solution. 

The  Gravity  Cell. — In  the  gravity  cell  the  depolarizer  used  is  sulphate  of 
copper  (solution).  Fig.  2  shows  the  usual  type  of  gravity  cell  used  in  telegraph 
and  telephone  work.  In  the  bottom  of  the  glass  containing-jar  is  placed  a 
"star"  of  copper  sheet,  attached  to  which  is  a  well-insulated  wire  extending 
out  of  the  top  of  the  jar  for  the  purpose  of  making  terminal  connection.  A 
portion  of  about  3  Ib.  of  blue- vitriol  (sulphate  of  copper)  is  placed  in  the  bottom 
of  the  jar,  being  well  distributed  around  the  copper  element  and  almost  cover- 
ing it.  The  vitriol  crystals  used  should  be  broken  up  so  that  none  of  those 


PRIMARY  BATTERIES 


15 


placed  in  the  jar  are  larger  than  a  walnut.  The  fine  particles  or  dust  of  vitriol 
should  not  be  used.  The  zinc  which  is  provided  with  a  hanger  is  then  suspended 
from  the  upper  edge  of  the  jar  and  the  jar  filled  to  within  a  half  inch  or  so  of 
the  top  with  pure  soft  water.  Clean  rain  water,  if  available,  is  the  best  for  the 
purpose.  Impure  or  hard  water  prevents  proper  action  of  the  chemicals  and 
should  not  be  used.  When  a  cell  is  first  set  up  it  is  customary  to  hasten  its 
action  by  " short  circuiting"  the  copper  and  zinc  terminals  by  means  of  a  short 
piece  of  wire.  In  a  short  time  zinc  sulphate  is  formed  around  the  zinc,  and  a 
copper  sulphate  solution  forms  around  the  copper,  the  two  fluids  being  sepa- 
rated because  of  their  different  specific  gravities. 
A  cell  in  good  condition  shows  a  fairly  clear  line 
of  demarcation  between  the  two  solutions.  The 
zinc  sulphate  appears  to  float  on  the  top  of  the 
denser  copper  solution  beneath.  If  the  circuit 
connecting  the  terminals  of  the  cell,  or  of  the 
battery  of  which  the  cell  forms  a  part,  is  left  open 
and  the  cell  not  called  upon  to  do  enough  work  to 
prevent  mixing  of  the  solutions,  the  copper  sul- 
phate gradually  comes  into  contact  with  the  zinc 
and  is  decomposed,  forming  cupros  oxide  (CuO) 
which  completely  covers  and  adheres  to  the  zinc. 
In  appearance  this  deposit  resembles  black  mud. 
Crystallization  of  the  zinc  sulphate  is  evidenced 
by  the  formation  of  salt-like  crystals  which  creep 
over  the  upper  edges  of  the  jar  and  down  its  sides, 
and  unless  periodically  cleaned  away,  in  a  com- 
paratively short  time  make  a  disagreeable  mess 
on  battery  shelves.  To  prevent  the  creeping  of  salts  over  the  tops  of  jars  a 
mineral  oil  of  high  viscosity  is  sometimes  applied  by  pouring  it  over  the  top 
of  the  solution  to  a  depth  of  1/16  to  1/8  of  an  inch. 

The  specific  gravity  (sp.  gr.)  of  water  has  been  assigned  the  value  of  i.co, 
and  the  density  or  weight  of  all  other  liquids  is  measured  in  comparison  there- 
with. Sulphuric  acid  has  a  sp.  gr.  of  1.84,  mercury  13.58,  etc.  For  the  practi- 
cal measurement  of  the  specific  gravity  of  a  liquid  an  instrument  called  a  hy- 
drometer is  used  (see  Fig.  3).  This  instrument  consists  of  a  hollow  sealed  glass 
tube  or  float,  weighted  at  its  lower  extremity  with  lead  shot,  the  stem  of  the 
float  being  provided  with  a  graduated  scale.  When  a  hydrometer  is  allowed 
to  float  freely  in  a  liquid,  the  division  of  the  scale  on  a  level  with  the  surface  of 
the  liquid  indicates  the  specific  gravity  of  the  liquid  so  tested.  There  are  two 
or  three  different  makes  of  scale,  but  the  one  generally  used  is  known  as  the 
Baume  scale  which  registers  divisions  from  o  to  45.  When  a  gravity  cell  is 
at  its  best  the  scale  will  sink  to  20°.  Should  a  test  show  that  the  density  of  the 
solution  is  below  5°  or  above  25°  the  cell  is  not  in  good  condition.  It  is  when 


FIG.  2. — Gravity  cell. 


16 


AMERICAN  TELEGRAPH  PRACTICE 


the  density  of  the  zinc  solution  rises  above  25°  that  the  crystallization  of  the 
zinc  sulphate  is  most  active.  Obviously,  the  remedy  is,  as  indicated  above, 
to  short  circuit  the  cell  until  the  chemical  action  has  had  an  opportunity  to 
restore  normal  conditions;  that  is,  when  the  impoverished  condition  of  the 
cell  is  the  result  of  having  been  left  on  "open  circuit"  for  an 
unreasonable  length  of  time. 

In  the  installation  and  maintenance  of  gravity  batteries 
there  are  a  few  points  of  sufficient  practical  importance  to 
warrant  consideration  here. 

It  is  of  considerable  benefit  to  have  jars  well  cleaned  and 
dried  before  being  used  in  setting  up  cells. 

The  insulated  conductor  leading  from  the  copper  should  in 
each  case  be  securely  riveted,  making  solid  contact. 

It  is  not  good  practice  to  attempt  to  renew  impover- 
ished cells  by  occasionally  dropping  in  a  few  crystals  of 
bluestone. 

Cells  in  service  should  frequently  be  tested  with  the 
hydrometer.  In  case  the  specific  gravity  rises  above  25°, 
additional  soft  water  should  be  added.  To  do  this,  some  of 
the  zinc  solution  may  be  removed  by  means  of  a  rubber-tube 
syphon.  The  rubber  tube  used  for  this  purpose  should  be 
kept  clean. 

Battery  shelves  should  be  kept  scrupulously  clean. 
If  the  insulating  material  surrounding  the  wire  leading  from 
the  copper  becomes  cracked,  the  wire  should  be  replaced  with 
one  properly  insulated. 

Cells  should  be  renewed  when  the  original  charge  of  blue- 
vitriol  is  nearly  exhausted  or  when  the  two  solutions  have 
become  too  intimately  merged. 

Gravity  cells  should  be  disturbed  as  little  as  possible. 
When  a  cell  is  for  any  reason  taken  down  and  there  is 
enough  of  the  zinc  remaining  to  warrant  using  it  again,  it 
should  be  cleaned  off  while  wet  as  the  deposits  harden  very 
quickly  and  later  are  difficult  to  remove. 

Coppers  may  be  cleaned  by  laying  the  plates  separately  on 
a  hard  surface  and  hammering  off  the  deposits. 

The  temperature  of  a  battery  room  should  not  be  permitted 
to  get  below  60°  F. 

The  rapidity  with  which  the  materials  of  a  cell  are  consumed  depends  upon 
the  amount  of  work  done  by  it — upon  the  quantity  of  electricity  per  unit  of 
time  that  it  is  required  to  supply.  The  consumption  and  deposition  of  the 
materials  used  in  gravity  cells  per  ampere-hour,  in  fractions  of  an  avoirdupois 
pound,  and  from  which  the  cost  of  producing  a  given  current  may  be  ascer- 


FIG.  3. 
Hydrometer. 


PRIMARY  BATTERIES 


17 


tained,  theoretically,  when  the  price  of  the  materials  is  known,1  may  be  cal- 
culated from  the  following  table: 


Material 

Atomic  weight 

Pounds,  per  ampere- 
hour 

Zinc  consumed 

64.  o 

o  0026749 

Sulphate  of  copper  consumed  
Copper  deposited                            .            

249-5 
63  .  o 

0.0102810 
o.  002^040 

In  the  computation  the  copper  deposited  is  a  credit. 

The  electrochemical  equivalent  of  zinc  is  here  taken  as  0.00033696 
grm.  per  ampere-second  according  to  the  determinations  of  Rayleigh  and 
Kohlrausch. 

The  average  life  of  a  cell  used  for  furnishing  current  for  "local"  circuits, 
that  is,  sounders  and  multiplex  and  repeator  locals,  is  from  five  to  eight  weeks, 
a  main-line  battery  supplying  one  or  more 
main-line  wires  two  months,  and  a  duplex  or 
quadruplex  battery  about  six  months.  These 
estimates  presuppose  intelligent  and  careful 
supervision  of  the  batteries  so  employed.  A 
space  interval  of  at  least  3/4  in.  should  be 
maintained  between  individual  cells  on  a  shelf. 
It  is  extremely  important  to  have  all  connec- 
tions between  cells  and  of  battery  terminals 
tight  and  secure. 

The  Leclanche  Cell.— The  Leclanche  cell 
is  not  used  in  the  operation  of  telegraph  lines 
but  it  has  an  extensive  general  employment  in 
operating  signaling  bells,  telephones,  etc.,  and 
for  that  reason  its  action  and  assembly  should 
'be  understood.  A  familiar  form  of  this  type 
of  battery  is  shown  in  Fig.  4.  The  cell  con- 
sists of  a  glass  containing-jar  about  half  the 
size  of  that  used  for  the  gravity  cell,  a  porous- 
cup  containing  a  plate  or  rod  of  carbon  (the  in- 


FIG.  4. — Leclanche  cell. 


active  element)  and  a  zinc  pencil  (the  positive  element).  The  exciting  liquid 
is  a  salammoniac  solution  in  which  the  zinc  dissolves,  forming  a  double  chloride 
of  zinc  and  ammonia,  while  at  the  same  time  ammonia  gas  and  hydrogen  are 
liberated  at  the  carbon  plate  contained  in  the  porous-cup.  The  depolarizer  is 
black  binoxide  of  manganese,  small  pieces  of  which  are  mixed  with  powdered 
carbon  and  the  mixture  thus  formed  packed  around  the  carbon  rod  within  the 

1  F.  L.  Pope,  "The  Electric  Telegraph,"  p.  74. 
2 


18 


AMERICAN  TELEGRAPH  PRACTICE 


porous-cup.  As  a  depolarizing  agent  the  oxide  of  manganese  slowly  gives  up 
oxygen  as  required.  The  porous-cup  does  not  prevent  the  passage  of  current, 
but  protects  the  zinc  from  the  action  of  the  oxide. 

The  constituent  materials  of  the  porous-cup  are:  feldspar,  8  parts;  ball  clay, 
6  parts;  kaolin,  9  parts;  and  2  parts  quartz — the  latter  is  added  for  the  purpose 
of  giving  the  mixture  the  required  mechanical  strength.  The  mass  is  then  pul- 
verized, mixed  with  water  and  boiled  for  24  hours,  after  which  it  is  moulded 
into  cups  of  the  desired  dimensions  and  baked  in  a  dry  kiln  at  a  tempera- 
ture of  i, 800°  F.,  for  a  period  of  24  hours. 

If  left  on  short  circuit  or  worked  hard,  it  is  impossible  to  entirely  prevent 
polarization,  but  after  showing  signs  of  polarization,  if  the  cell  is  left  on  open 
circuit  for  a  short  time  it  rapidly  recuperates.  It  is  best  not  to  use  a  sal- 
ammoniac  solution  too  strong,  as  crystals  will  gather  on  the  zinc  and  thus 

reduce  the  surface  of  the  zinc  exposed 

to  the  solution.  On  the  other  hand, 
if  the  solution  is  too  weak,  chloride  of 
zinc  will  form  on  the  zinc  element. 
Either  of  these  conditions  consider- 
ably increases  the  internal  resistance 
of  the  cell.  As  in  the  gravity  cell, 
soft  clean  water  should  be  used  in 
forming  the  solution.  About  6  oz.  of 
salammoniac  is  sufficient  per  cell,  and 
water  should  be  added  until  the  jar  is 
filled  to  within  3/4  in.  of  the  top  of  the 
jar.  The  solution  should  be  stirred 
until  the  salammoniac  has  dissolved. 
The  upper  part  of  the  carbon  cylinder 
or  porous-cup  should  be  kept  clean  and 
dry  in  order  to  prevent  leakage  of  cur- 
rent between  the  poles.  To  renew  the 
cell,  all  that  is  necessary  is  to  clean  or 
renew  the  zinc  element  and  pour 
some  fresh  solution  into  the  jar.  The 
FIG<  s.— Fuller  cell.  carbon  is  the  negative  element  of  the 

cell  and  the  positive  pole;  the  zinc  is 
the  positive  element  and  the  negative  pole. 

The  Fuller  Cell. — There  are  several  forms  of  this  type  of  battery,  but  the 
action  of  and  the  assembly  of  the  various  forms  is  practically  the  same.  This 
c"eU  is  sometimes  referred  to  as  the  bichromate  cell  because  of  the  employment  of 
.  bichromate  of  potash  together  with  a  dilute  sulphuric  acid  solution  as  the  elec- 
trolyte. The  bichromate  chemically  unites  with  the  hydrogen  and  prevents 
polarization.  A  common  type  of  Fuller  cell  is  shown  in  Fig.  5. 


PRIMARY  BATTERIES 


19 


A  well-amalgamated  block  of  zinc  is  placed  in  a  porous-cup  which  is  nearly 
filled  with  a  dilute  solution  of  sulphuric  acid.  The  cup  is  placed  in  the  center 
of  a  glass  jar  about  the  size  of  a  Standard  gravity  jar.  A  carbon  plate  of  com- 
paratively large  section  is  placed  in  the  jar  at  one  side  of,  or  completely  sur- 
rounding the  porous-cup.  The  containing  vessel  is  then  filled  to  within  1/2 
in.  of  the  top  with  a  solution  of  potassium  bichromate".  It  is  customary  to  keep 
a  spoonful  or  so  of  mercury  in  the  bottom  of  the  porous-cup  so  that  the  amal- 
gamation of  the  zinc  contained  therein  may  be  continuously  renewed. 

The  bichromate  solution  (electropoin)  is  made  up  of  i  part  sulphuric  acid, 
3  parts  bichromate  of  potash,  and  9  parts  water.  The  bichromate  should  be 
dissolved  in  warm  water  and  when  cool  the  required  amount  of  sulphuric  acid 
should  be  slowly  added.  The  reverse  process  should  never  be  attempted; 
that  is,  the  bichromate  solution  should  not  be  poured  into  the  sulphuric  acid, 
as  excessive  heat  and  distressing  fumes  will  thereby 
be  generated.  When  first  set  up  the  solution  is 
of  a  light  brown  color  and  as  it  ages,  gradually 
turns  darker. 

As  the  internal  resistance  of  this  cell  is  but 
0.5  ohm  and  its  e.m.f.  2  volts,  it  is  an  unusually 
powerful  source  of  current  and  it  has  many  uses, 
especially  when  it  can  be  employed  where  intelli- 
gent handling  may  be  availed  of.  It  is  always 
inadvisable  to  allow  any  but  careful  attendants 
to  handle  destructive  acids. 

The  Edison-Lalande  Cell. — This  cell  is  capa- 
ble of  yielding  a  large  current — as  much  as  30 
amperes  on  short  circuit,  due  to  its  low  internal 
resistance  and  relatively  high  e.m.f.,  0.75  volt. 

The  cell  is  made  up  of  zinc  and  copper  oxide 
in  a  solution  of  caustic  potash.  As  usually  con- 
structed the  plates  are  hung  side  by  side  from 
the  cover  of  the  jar.  The  copper  oxide  is  plated 
with  a  film  of  copper  for  the  purpose  of  reducing 
the  initial  resistance  of  the  cell,  and  is  held  in  a 

frame  suspended  from  the  cover.  To  prevent  the  inevitable  creeping  of  salts, 
a  film  of  oil  is  poured  on  top  of  the  solution.  When  the  solution  is  being 
mixed  the  caustic  potash  should  not  be  placed  in  the  cell  and  left  to  dissolve 
as  it  is  very  likely  to  solidify  at  the  bottom  of  the  jar.  The  solution  should  be 
stirred  until  all  of  the  potash  is  dissolved.  As  the  solution  used  in  this  battery 
will  burn  the  skin  and  clothing,  great  care  should  be  exercised  when  stirring,  to 
avoid  splashing.  In  renewing  the  Lalande  cell  a  new  solution  should  be  set  up 
at  the  time  the  zincs  and  oxides  are  renewed.  The  solution  should  always 
reach  to  the  lower  colored  line  in  the  jar,  after  it  has  cooled  down;  usually  it 


FIG.  6. — Edison-Lalande  cell. 


20 


AMERICAN  TELEGRAPH  PRACTICE 


is  found  necessary  to  add  a  little  water  to  bring  it  up  to  this  line  after  the 
cooling  process.  Fig.  6  shows  a  view  of  an  assembled  Edison-Lalande  cell. 

The  Dry  Cell. — Generally  speaking,  dry  cells  are  modifications  of  the  sal- 
ammoniac  cell,  in  which  the  water  is  replaced  by  one  of  the  various  gelatinous 
substances  available  for  the  purpose.  The  Gassner  cell,  one  of  the  original 
dry-cell  products,  embodied  a  paste  made  of  i  part  oxide  of  zinc,  i  part  sal- 
ammoniac,  3  parts  plaster,  i  part  zinc  chloride,  and  2  parts  water,  all  by  weight. 

Fig.  7  shows  a  typical  construction  of  dry 
cell  as  at  present  manufactured  in  this 
country. 

In  making  up  dry  cells  a  zinc  cylinder 
is  lined  on  the  inside  with  blotting  paper  or 
an  absorbent  cardboard.  The  exciting  fluid 
is  poured  into  the  cylinder  and  left  for  a 
period  of  15  minutes  to  soak  thoroughly. 
The  electrolyte  is  then  poured  out  and  the 
-Blotting Paper  cylinder  mverted  so  that  the  surplus  liquid 
may  drain  off.  The  carbon  rod  is  then 
inserted  and  the  space  between  it  and  the 
sides  of  the  absorbent  paper  is  filled  with 

.  7. — Dry  cell.  the  depolarizer  which  usually  consists  of 

black  oxide  of  manganese  and  granulated 

carbon,  this  mixture  is  moistened  with  the  electrolyte  before  placing  it  in  the 
shell.  On  the  surface  a  layer  of  dry  sand  is  placed  and  on  the  top  of  this  hot 
pitch  is  poured  and  allowed  to  harden.  The  function  of  the  depolarizer  is  to 
furnish  a  supply  of  oxygen  required  to  keep  up  combustion.  After  the  cell 
has  been  short  circuited  for  a  brief  period  or  worked  hard  for  a  considerable 
length  of  time  the  oxygen  in  the  depolarizer  is  consumed,  the  latter  gradually 
hardens  and  the  pores  close  up.  When  the  oxygen  is  gone  the  cell  ceases  to 


•  Pitch 


g Pasteboard 


-  line 


Filling 


Carbon 


FIG.  8. — Arrangement  of  dry  cells  on  shelf. 

be  of  value  as  a  generator  of  electricity.  The  electrical  output  of  a  dry  cell,  as 
well  as  its  length  of  life  for  a  stated  output  is,  in  large  measure,  dependent 
upon  the  dimensions  of  the  exposed  areas  of  the  zinc  and  carbon. 

An  important  consideration  in  the  manufacture  of  dry  cells  is  the  thickness 
of  the  zinc  strip  used  in  forming  the'shell.  The  plate  employed  for  the  purpose 
ranges  in  thickness  from  0.014 in-  to  0.02 5  in.  The  former  will  be  eaten  through 
much  more  quickly  than  the  thicker  plates  and  the  result  is  that  the  life  of  the 


PRIMARY  BATTERIES 


21 


cell  is  considerably  shortened  on  account  of  the  moisture  oozing  out  and  soaking 
into  the  cardboard  casing.  If  two  adjacent  cells  are  thus  affected  and  the  wet 
sides  come  into  contact  an  effectual  short  circuit  is  established  which  may 
destroy  the  efficiency  of  an  entire  battery.  One  method  of  overcoming  this 
is  to  use  pasteboard  covers  which  have  been  boiled  in  a  mixture  half  beeswax 
and  half  paraffine.  It  is  good  practice  in  arranging  dry-cell  batteries  on  shelves 
to  set  the  cells  a  half  inch  or  so  apart  and  in  the  manner  shown  in  Fig.  8  in  order 
to  prevent  any  possibility  of  short  circuit. 

Standard  Cells.— In  determining  the  absolute  value  of  a  standard  e.m.f., 
instead  of  depending  upon  the  accuracy  of  a  measuring  instrument  to  register 
values,  a  standard  cell  constructed  from  definite  specifications  is  used. 

Three  types  of  cell  which  have  been  used  for  the  purpose  are  the  Clark, 
the  Carhart-Clark,  and  the  Weston  cell. 


Crystals 
Amalgam 


feiH  3.  Solution 


Crystals 
Paste 

Mercury 


FIG.  ga. — Clark  standard  cell. 


FIG.  gb. — Weston  standard  cell. 


The  Electrical  Congress  held  in  Chicago  in  1893  adopted  the  Clark  cell  as 
the  international  standard  of  e.m.f.  In  this  cell  the  positive  element  is  mercury, 
the  negative  amalgamated  zinc,  and  the  electrolytes  saturated  solutions  of 
sulphate  of  zinc  and  mercurous  sulpate.  At  a  temperature  of  15°  C.,  the 
e.m.f.  is  1.434  international  volts. 

The  Carhart-Clark  Cell. — This  cell  embodies  the  same  elements  as  the 
Clark,  but  the  solution  of  zinc  sulphate  is  saturated  at  o°  C.,  the  e.m.f.  being 
1.440  volts. 

Weston  Cadmium  Cell. — The  elements  of  this  standard  cell  are  cadmium 
and  mercury  and  the  electrolytes  sulphates  of  cadmium  and  mercury. 

On  January  i,  1911,  the  Bureau  of  Standards  at  Washington  adopted 
a  new  value  for  the  electromotive  force  of  the  Weston  cell,  namely,  E  = 


22  AMERICAN  TELEGRAPH  PRACTICE 

1.01830  international  volts  at  20°  C.  This  change  was  made  pursuant  to 
official  definitions  of  values  adopted  by  the  International  Electrical  Congress 
held  in  London  in  1908.  As  compared  with  the  standard  e.m.f.  previously 
employed,  the  change  is  equivalent  to  an  increase  of  about  0.08  of  i  per  cent, 
in  the  value  of  the  international  volt. 

The  usual  form  of  constructidn  of  the  glass-containing  vessel  of  the  Clark 
standard  cell  is  shown  in  Fig.  g-a,  and  that  of  the  newer  type  of  Weston  cell  in 
Fig.  9-6. 

This  is  called  the  "H"  form  of  cell.  This  type  is  quite  easily  filled,  permit- 
ting the  contents  of  each  leg  rapidly  to  take  on  the  normal  temperature  of  the 
bath.  A  2-mm.  platinum  wire  is  sealed  in  each  leg,  the  tips  being  flattened 
flush  with  the  glass,  making  good  contact  with  the  mercury  or  amalgams.  The 
mercury,  amalgam  and  paste  each  have  a  depth  of -from  10  to  15  mm.  Some 
crystals  are  placed  above  the  paste,  and  on  top  of  the  amalgam  a  layer  of  crys- 
tals is  laid  to  a  depth  of  10  mm.  The  cell  is  filled  to  the  top  of  the  cross  tube 
with  the  saturated  solution.  The  Weston  cell  has  a  temperature  coefficient  of 
about  one-thirtieth  of  that  of  the  Clark  cell.  This,  however,  is  not  of  great 
importance  as  the  cells  are  maintained  in  a  bath  the  temperature  of  which  is 
automatically  controlled.  The  electromotive  force  of  these  standard  cells  is 
quite  constant,  but  decreases  slightly  with  age.  Fifteen  cells  in  use  in  the  lab- 
oratories of  the  Bureau  of  Standards  have  on  the  average  decreased  one-ten 
thousandth  of  a  volt  in  four  years. 


CHAPTER  III 

DYNAMOS,   MOTORS,   MOTOR-GENERATORS,   DYNAMOTORS, 
VOLTAGE  AND  CURRENT  REGULATORS 

Electro-mechanical  Generators  of  Electricity. — These  at  the  present  time 
are  used  quite  extensively  to  furnish  current  for  the  operation  of  telegraph 
lines,  also  for  the  operation  of  terminal  apparatus  including  main-line  and 
local  instruments. 

In  some  instances  current  furnished  by  commercial  power  companies  is 
used  directly,  being  supplied  by  one  or  more  pairs  of  wires  from  the  power  sta- 
tion to  the  telegraph  office ;  there  the  current  is  distributed  to  the  various  cir- 
cuits by  means  of  switching  systems. 

In  general,  however,  the  operation  of  telegraph  circuits  requires  the  employ- 
ment of  different  voltages,  ranging  about  as  follows:  40  volts,  85  volts,  125 
volts,  200  volts,  and  375  volts.  Further,  it  is  necessary  that  at  least  the  two 
last  named  voltages  be  available  in  both  negative  and  positive  polarities. 

Regardless  of  considerations  of  economy,  the  usual  practice  is  to  gen- 
erate on  the  ground  (in  the  telegraph  office)  the  different  values  of 
potential  required  in  each  individual  installation.  There  are  two  ways  in 
which  the  desired  end  may  be  accomplished.  One  way  is  to  set  up  a  number 
of  dynamos  capable  of  generating  like  values  of  e.m.f.,  and  to  connect  a  suffi- 
cient number  of  them  in  series  to  produce  an  aggregate  voltage  equal  to  the 
maximum  required.  If,  then,  the  units  are  arranged  in  multiples  of  40  volts, 
potentials  of  the  following  specified  values  may  be  tapped  off :  40  volts,  80 
volts,  120  volts,  1 60  volts,  200  volts,  240  volts,  280  volts,  320  volts,  360 
volts,  and  400  volts.  That  is,  in  order  to  provide  voltages  ranging  from  40 
to  400  in  multiples  of  40  volts,  ten  dynamos  are  required.  It  is  obvious  that 
a  series  of  machines  so  connected  would  all  be  of  one  polarity,  either  negative 
or  positive,  and  that  a  duplicate  set  of  machines  having  identical  ranges  of 
voltage  are  required  to  supply  the  opposite  polarity.  Where  this  method  is 
employed  it  is  customary  to  have  in  readiness  a  third  group  of  machines  as  re- 
serve and  so  connected  through  switches  that  either  polarity  may  be  availed  of. 

Another  method  is  to  make  use  of  generators  having  different  individual 
voltage  outputs.  That  is,  one  dynamo  for  each  polarity  of  each  voltage  re- 
quired. 

In  either  case  an  external  source  of  power  is  required  to  drive  the  dynamos, 
and  the  customary  method  of  driving  these  machines  is  through  the  medium 
of  electric  motors  mechanically  connected  to  the  rotating  elements  of  the 

23 


24  AMERICAN  TELEGRAPH  PRACTICE 

dynamos.  The  chief  advantage  of  this  arrangement  is  that  any  available 
commercial  voltage  whether  it  be  direct  current  or  alternating  current,  or 
whether  the  potential  is  no  volts,  220  volts  or  500  volts,  may  be  employed 
to  operate  the  motors  and  still  the  e.m.f.  of  each  dynamo  driven  by  its  re- 
spective motor  will  accord  with  its  rated  output.  One  dynamo  delivering  40 
volts,  another  85  volts,  another  200  volts,  and  so  on. 

What  follows  in  regard  to  the  construction  of  and  operation  of  dynamos 
includes  only  such  detail  as  seems  necessary  to  adequately  present  the  subject, 
from  a  telegraph  standpoint. 

In  a  dynamo  an  e.m.f.  is  induced  in  wires  caused  to  move  through  the 
magnetic  field  near  the  poles  of  a  magnet.  The  magnetic  field  is  the  space 
about  the  magnet  within  which  a  piece  of  iron  would  be  attracted  to  or 
repelled  from  it.  The  direction  and  strength  of  the  magnetic  force  causing 
this  attraction  or  repulsion  is  determined,  and  a  certain  unit  value  selected; 
called  a  line  of  force;  by  which  the  intensity  of  the  magnetic  field  can  be 
measured.  The  total  number  of  lines  of  force  issuing  from  the  magnet  is 
called  its  magnetic  flux. 

The  value  of  the  e.m.f.  induced  in  the  wires  referred  to  depends  upon  the 
number  of  lines  of  force  they  cut  in  a  certain  time,  that  is,  upon  the  "rate" 

at  which  the  lines  of  force  are  cut.  If 
the  wires  are  simply  held  in  the  mag- 
netic field,  no  e.m.f.  is  generated.  Either 
one  must  move  with  respect  to  the  other 
if  an  e.m.f.  is  to  be  produced  in  the  wires. 
If  the  wires  move  through  the  field  in 

one  direction,  the  e.m.f.  produced  will 
ric.  10. — Dynamo  field-magnet  poles.  ,  „        .          ,.         . 

cause  the  current  to  now  in  a  direction 

the  reverse  of  that  resulting  from  moying  the  wires  in  the  opposite  direction. 
Also,  the  direction  of  the  current  in  the  wire  moving  under  a  north  pole  is  op- 
posite to  that  of  the  current  in  the  wire  moving  under  the  south  pole  of  a 
magnet. 

Figure  10  shows  the  poles  of  a  pair  of  electromagnets,  one  marked  N 
(north)  the  other  S  (south).  The  dotted  lines  represent  lines  of  force 
(shown  thus  for  the  purpose  of  clearness)  streaming  across  the  gap  in  a  direc- 
tion from  north  pole  to  south  pole.  The  armature  is  represented  as  a  single 
loop  of  wire  A,  with  its  ends  B  and  C  brought  out  at  one  side.  If  the  loop  is 
revolved  in  the  direction  indicated  by  the  curved  arrow  it  passes  through  the 
lines  of  force  and  an  electric  current  is  induced  in  the  loop  flowing  in  the  direc- 
tion shown  by  the  straight  arrows.  As  the  coil  is  moved  through  a  complete 
revolution  it  is  evident  that  each  side  of  it  will  come  within  the  influence  first 
of  one  pole  and  then  of  the  other  thus  reversing  the  direction  of  the  current  in 
the  loop  twice  during  each  complete  revolution.  The  result  is  that  alternat- 
ing current  is  produced  in  the  armature  coil,  that  is,  current  which  alternates 


DYNAMOS,  MOTORS  AND  MOTOR-GENERATORS  25 

in  polarity  from  positive  to  negative  and  negative  to  positive  as  indicated 
above. 

If  an  alternating  current  is  desired  the  terminals  of  the  armature  coil  (or 
coils)  are  connected  with  "collector"  rings  which  are  mounted  on  one  end  of 
the  armature  shaft  and  separately  insulated  from  it,  the  current  being  taken 
off  by  means  of  carbon  brushes,  one  in  contact  with  each  collector  ring  and 
mounted  in  stationary  brush  holders  to  which  the  wires  of  any  external  cir- 
cuit may  be  connected. 

When  a  unidirectional  or  direct  current  is  required,  as  is  usual  in  tele- 
graphy, it  is  necessary  to  use  a  commutator  in  order  to  take  from  one  of  the 
brushes  a  constant  positive  current  and  from  the  other  a  constant  negative 
current. 

Figure  u  illustrates  the  end  view  of  a  commutator  having  a  number  of 
insulated  segments  to  which  the  ends  of  individual  armature  coils  may  be 
attached.     In  the  figure  one  coil  only  is  shown.     The  brushes  which  serve  to 
lead  the  current  away  from  the  dynamo  to  any  desired  external  circuit  are 
shown  in  position/     The  com- 
mutator is  built  in  the  form  of 
a  sleeve  or  ring  and -mounted 
on    one   end  of  the  armature 
shaft.     The  commutator  C  is 
built   up   of   strips  of  copper, 
forming  segments  S,  S,  all  in-         B 
sulated   from   each  other,  the 
entire  commutator  being  insu- 
lated    from    the    shaft    upon 
....       .       .   .  FIG.  ii. — End  view  of  commutator,  showing  one 

which  it     is  rigidly    mounted.  armature  coil. 

Remembering  that  the  coil  W 

is  mounted  on  the  armature  and  that  it  is  revolved  between  the  poles  of  an 
electromagnet,  if  we  consider  that  the  coil  terminal  E  is  positive  at  the  in- 
stant shown,  a  positive  current  may  be  taken  from  brush  B.  But,  as  the 
coil  is  moved  around  one-half  revolution,  the  current  in  it  reverses  and  the 
terminal  F  being  then  in  contact  with  brush  B  delivers  at  that  point  a  posi- 
tive current.  This  must  be  so  as  the  brushes  are  stationary,  and  the  pole 
pieces  of  the  electromagnets  are  stationary  and  when  the  terminal  F  comes 
into  contact  with  brush  B  it  must  necessarily  be  in  the  same  position  in  the 
magnetic  field  as  terminal  E  was  when  in  contact  with  brush  B. 

Dynamo  Fields. — In  the  various  types  of  dynamos  manufactured  at  the 
present  time,  three  varieties  of  field-magnet  iron  are  used,  namely,  cast-iron, 
cast-steel,  and  sheet-steel.  It  has  been  determined  that  a  greater  number  of 
lines  of  force  can  be  produced  with  a  certain  magnetizing  force  in  a  given  sec- 
tion of  sheet-steel  than  in  similar  sections  of  cast-steel  or  cast-iron.  From 
the  standpoint  of  magnetic  permeability,  mild  steel  is  next  in  order  and  then 


26  AMERICAN  TELEGRAPH  PRACTICE 

follows  cast-iron.  The  coils  of  insulated  wire  wound  around  the  pole  pieces  of 
a  dynamo  constitute  the  field  winding.  The  purpose  of  these  coils  is  to  con- 
duct a  current  of  electricity  through  them  in  order  to  inductively  magnetize 
the  poles.  The  amount  of  magnetism  generated  is  dependent  upon  the  num- 
ber of  turns  of  wire  in  the  field  coils  and  upon  the  volume  of  current  which  is 
passed  through  these  coils. 

As  was  brought  out  under  the  heading  of  current  in  Chapter  I,  the 
practical  unit  of  current  is  the  ampere.  Although  the  subject  of  electro- 
magnets will  be  taken  up  in  detail  in  a  later  chapter,  it  may  here  be  stated 
that  the  unit  of  magnetizing  force  is  the  ampere-turn,  which  signifies  that 
i  ampere  of  current  is  flowing  in  i  turn  of  wire  wound  around  the  core  of  a 
magnet.  The  total  magnetizing  force  is  determined  by  multiplying  the 
number  of  turns  of  wire  wound  around  the  core  of  a  magnet  by  the  number 
of  amperes  flowing  in  the  circuit  thus  formed.  An  equal  number  of  lines 
of  force  are  generated  by  i  ampere  flowing  in  50  turns  as  by  50  amperes  flow- 
ing in  i  turn,  or  as  2  amperes  in  25  turns.  The  product  of  the  turns  and 
the  amperes  determines  the  total  magnetism  developed.  The  factors  may 
have  any  value  provided  the  product  is  equal;  or,  T  =  tXl.  Where  T  rep- 
resents the  ampere  turns,  /  the  number  of  turns  of  wire  and  7  the  current 
in  amperes,  flowing. 

Field  Excitation  of  Dynamos. — The  field  magnets  of  dynamos  may  be 
energized  either  by  current  from  some  external  source  or  by  current  taken 
from  the  commutator  brushes  of  the  machine  itself.  When  an  external 
source  of  current  is  used,  it  is  immaterial,  theoretically,  whether  it  is  a  primary 
battery,  storage  battery,  or  an  independent  dynamo,  provided  the  current 
supplied  is  unidirectional. 

In  the  smaller  makes  of  dynamos,  such  as  those  used  in  furnishing  tele- 
graph currents,  the  self-excited  dynamo  is  the  type  generally  used.  Self- 
excited  generators  may  be  either  series  wound,  shunt  wound,  or  compound 
wound. 

Series-wound  generators  deliver  a  voltage  which  increases  with  the  load. 

Shunt-wound  generators  deliver  approximately  constant  voltage. 

Compound-wound  generators  deliver  constant  voltage. 

In  series-wound  closed-coil-armature  generators  the  entire  field  winding 
is  in  series  with  the  armature,  and  consequently  the  field  coils  carry  the 
entire  current  generated. 

Figure  12  in  simple  lines  shows  the  wiring  of  a  bi-polar  series- wound 
dynamo. 

In  a  shunt-wound  dynamo  the  field  winding  is  connected  to  the  brushes 
in  the  manner  illustrated  in  Fig.  13.  A  field  regulating  rheostat  is  inserted 
as  shown. 

A  compound-wound  generator  as  shown  in  Fig.  14  is  provided  with  a 
shunt  field  winding  connected  to  the  brushes  in  series  with  a  rheostat  and 


DYNAMOS,  MOTORS  AND  MOTOR-GENERATORS 


27 


with  a  second  winding  connected  in  series  with  the  armature.  At  no-load 
the  shunt  winding  excites  the  machine  to  normal  voltage.  When  the 
external  circuit  or  load  is  applied,  the  field  excitation  is  strengthened  because 
of  the  current  then  allowed  to  flow  through  the  series  winding.  For  use  in 
telegraph  service  the  advantages  of  compound- wound  generators  is  apparent, 
as  the  auxiliary  series  winding  automatically  increases  the  strength  of  the 
field  in  response  to  load  increases,  and,  conversely,  reduces  the  field  strength 


FIG.  12. — Two-pole  series 
dynamo. 


FIG.  13. — Two-pole  shunt 
dynamo. 


FIG.   14. — Two-pole 
compound  dynamo. 


as  the  load  is  decreased,  thus  furnishing  practically  constant  voltage  regard- 
less of  variations  of  the  resistance  of  external  circuits  applied  to  it. 

Most  of  the  generators  built  for  telegraphic  purposes  during  the  past 
20  years  have  been  shunt  wound,  but  the  superior  advantages  of  compound- 
wound  machines  over  the  former  are  very  likely  to  result  in  a  more  general 
employment  of  compound-wound  machines  in  the  future.  It  is  possible 

that  their  general  employment  may  be  hastened     i 1 

by  having  some  of  the  machines  at  present  in  .- \ 

service  " compounded."  In  view  of  this  it 
seems  justifiable  to  devote  some  space  to  a  con- 
sideration of  the  principles  involved. 

Magnetic  Circuit. — The  magnetic  circuit  of 
a  dynamo  is  illustrated  by  the  dotted  lines  in 
Fig.  15.  The  circuit  includes  the  iron  cores 
of  the  field  coils,  the  iron  yoke  joining  these 
cores,  the  iron  core  of  the  armature,  and  the 
air  "gap"  between  the  pole  faces  and  the 
armature.  The  amount  of  m.m.f.  required  in 


FIG.     15. — Magnetic   circuit 
of  two-pole  dynamo. 


the  metallic  portion  of  this  circuit  is  directly  dependent  upon  the  magnetic 
strength  which  it  is  desired  to  develop.  This,  of  course,  is  infinitely  less 
than  that  required  to  set  up  magnetism  of  equal  density  in  an  equal 
length  of  air  space.  The  field  winding  must  be  designed  to  establish 
magnetism  in  the  air-gap  portion  of  the  magnetic  circuit,  because  that 


28  AMERICAN  TELEGRAPH  PRACTICE 

is  the  seat  of  action,  where  the  insulated  loops  of  wire  (the  armature)  are 
revolved,  and  where  the  e.m.f.  is  generated. 

As  previously  indicated  the  magnetomotive  force  required  to  establish 
this  magnetic  field  is  expressed  in  ampere-turns,  and  it  is  eVident  that  if  a 
small  current  only  is  to  be  used  for  field  excitation,  a  great  many  turns  of 
fine  wire  will  be  needed  in  the  field  coils,  while,  if  a  large  current  is  to  be  used, 
a  much  larger  wire  may  be  employed.  The  factor  which  in  large  measure 
determines  the  size  of  wire  which  should  be  used  in  the  shunt  winding  is  the 
heating  of  the  conductor.  In  practice  the  allowable  heat  limit  confines  the 
permissible  shunt  current  to  about  5  per  cent,  of  the  line  current. 

In  calculating  the  correct  shunt  winding,  a  magnetic  flux  should  be 
provided  for  which  will  develop  the  desired  e.m.f.  with  the  external  circuit 
open.  When  current  flows  in  the  armature  coils  a  counteraction  takes 
place  which  has  a  tendency  to  oppose  field  magnetization.  There  is  also 
a  slight  reduction  in  the  voltage  of  the  generator  due  to  resistance  "drop" 
in  the  armature.  If  the  line  conductor  is  wound  around  the  field  coils  a  few 
turns,  the  reverse  magnetomotive  force  developed  by  the  armature  is  neu- 
tralized and  the  strength  of  the  magnetic  field  restored  to  a  value  sufficient 
to  reestablish  normal  voltage  at  the  machine  terminals.  That  portion  of 
the  line  conductor  wound  over  the  shunt  winding  is  called  the  series  or 
compound  winding. 

By  this  arrangement  the  voltage  at  the  brushes  of  the  dynamo  may  be 
caused  to  increase  as  the  current  demand  made  upon  the  machine  is  increased. 
EVen  in  dynamo  manufacturing  plants  it  is  found  to  be  somewhat  difficult 
to  determine  accurately  the  number  of  turns  to  give  the  series  winding  of 
compound  machines  to  meet  given  conditions.  Usually  the  machine  is 
"over-compounded"  and  a  portion  of  the  current  shunted  by  means  of  a 
variable  resistance  placed  across  the  terminals  of  the  series  coil  until  the 
correct  Value  has  been  obtained. 

A  shunt-wound  dynamo  may  be  compounded  by  the  addition  of  a  series 
field  winding.  One  method  of  approximately  determining  the  number  of 
series  turns  required  is  to  run  the  generator  with  the  external  circuit  open, 
and  by  means  of  an  ammeter  measure  the  current  required  in  the  field  coils 
to  develop  normal  voltage,  then  throw  on  the  load  (close  the  external  circuit) 
and  alter  the  resistance  of  the  field  regulator  until  the  desired  voltage  is 
obtained.  If  simple  compounding  is  the  object  this  will  be  the  no-load 
voltage,  but  if  the  machine  is  to  be  over-compounded  the  voltage  will  be 
proportionately  larger.  Now  if  the  field  current  is  again  measured  and  the 
difference  noted  in  the  two  readings  of  field  current  multiplied  by  the  turns 
in  the  shunt  coil,  this  value  divided  by  the  number  of  amperes  of  current 
flowing  in  the  armature  will  give  the  number  of  turns  required  in  the  series 
coil. 

The  "  shunt"  winding  as  a  rule  consists  of  cotton-covered  wire  of  a  very 


DYNAMOS,  MOTORS  AND  MOTOR-GENERATORS 


29 


small  gage  wound  on  the  core,  next  to  the  yoke.  On  account  of  the  small 
size  of  conductor  used  the  resistance  is  quite  high  and  the  current  volume  in 
the  shunt  circuit  is  correspondingly  small.  The  " series"  coil  must  be  low 
in  resistance,  generally  less  than  half  that  of  the  armature,  and  should  be 
wound  on  the  end  of  the  cores 
nearest  the  armature  so  that 
the  maximum  magnetic  effect 
may  be  obtained  in  the  air 
gap. 

Armatures. — In  Fig.  10  the 
armature  is  represented  as  a 
single  loop  of  wire.  In  the 
construction  of  practical  dyna- 
mos each  loop  consists  of  a 
number  of  turns.  As  compared 
with  one  turn,  when  two  turns 

are  used  the  e.m.f.  is  doubled, 

'   FIG.  16.— Drum  wound  armature,  showing  one  coil. 

because  an  equivalent  voltage 

will  be  generated  in  each  turn  of  wire,  and  in  general  in  order  to  obtain  a 
given  constant  potential  the  loops  are  so  located  and  connected  with  respect 
to  each  other  that  each  turn  complements  and  adds  to  the  e.m.f.  generated 
by  all  other  loops. 

A  completed  armature  consists  of  a  core,  a  commutator,  and  a  winding. 
The  core  serves  to  support  the  winding  rigidly  in  position  and  also  acts  as  a 

conductor  of  the  magnetic  flux 
from  one  field  magnet  pole-face 
to  the  other. 

Armatures  may  be  either 
drum  wound  or  ring  wound, 
and  may  have  either  smooth 
cores  or  slotted  cores.  Fig.  16 
illustrates  a  method  of  placing 
the  armature  coil  on  a  smooth- 
core  drum  armature.  A  loop 
of  three  turns  is  shown  with  its 


FIG.  17. — Ring  wound  armature. 


terminals  brought  out  to  adjacent  commutator  segments. 

In  ring-wound  armatures  the  conductor  turns  are  wound  around  a  ring- 
shaped  core  (Fig.  17)  and  that  portion  of  each  turn  which  is  on  the  inside  of 
the  ring  is  practically  inactive.  Drum  wiring  obviates  this  " dead"  winding, 
as  in  the  drum  type  of  armature  each  section  of  every  conductor  is  on  the 
outside  of  the  core. 

Armatures  may  have  either  closed-coil  or  open-coil  windings.  The  former 
have  all  of  the  loops  (inductors)  interconnected  so  that  with  the  exception 


30 


AMERICAN  TELEGRAPH  PRACTICE 


of  that  period  when  a  certain  portion  of  the  winding  is  undergoing  commuta- 
tion, the  voltage  induced  in  each  inductor  is  adding  its  quota  of  energy  to 
the  maintenance  of  a  constant  potential  in  the  external  circuit.  Closed- 
coil  winding  also  effects  a  decided  advantage  in  reducing  sparking  at  brushes 
to  a  minimum. 

Open-coil  windings  provide  commutator  connection  with  the  inductors 
in  such  manner  that  voltage  produced  in  the  coils  is  made  use  of  only  when 
each  individual  coil  is  undergoing  commutation. 

Closed-coil  drum  windings  may  be  either  lap  wound  or  wave  wound,  the 
former  method  generally  requires  that  the  number  of  coils  on  the  armature 
be  the  same  as  the  number  of  bars  on  the  commutator,  and  the  number  of 

commutator  bars  employed  "even,"  to  permit 
of  equal  distribution  midway  between  the 
brushes,  while  wave  winding  advances  around 
the  commutator  similarly  to  the  manner  in  which 
a  "wave"  travels  progressively  from  point  to 
point. 

The  Commutator. — Fig.  18  shows  a  view  of 
a  commutator  disconnected  from  the  armature 
wiring  and  from  the  shaft. 

As  previously  stated,  the  current  generated 
in  an  individual  moving  armature  coil  alter- 
nates from  one  polarity  to  the  other  as  the  coil 
cuts  the  lines  of  force  passing  from  north  to 
south  pole  during  one-half  of  the  revolution, 
while,  as  stated  in  connection  with  Fig.  1 1 ,  during 
the  other  half  revolution  the  coil  cuts  the  lines 
of  force  in  the  reverse  direction. 

The  commutator  consists  of  a  number  of  copper  strips  or  segments,  each 
one  insulated  from  the  others  by  means  of  strips  of  a  high  grade  of  mica. 
Usually  the  number  of  segments  is  the  same  as  the  number  of  armature  coils, 
and  the  number  of  each  is  calculated  according  to  the  desired  output  of  the 
generator.  The  carbon  brushes  which  rest  upon  the  commutator  serve  to 
lead  the  current  from  each  coil  at  the  moment  it  attains  its  maximum  value. 
It  is  evident  that  the  current  gathered  by  the  brushes  will  be  "pulsating" 
in  character,  but  by  employing  a  large  number  of  coils  and  segments  the  cur- 
rent generated  is  so  nearly  uniform  that  the  pulsations  are  not  noticeable  in 
practical  operations. 


FIG.  18. — Commutator  re- 
moved from  armature  shaft. 


ELECTRIC   MOTORS 

Direct-current  Motors. — What  has  been  said  in  regard  to  the  various 
elements  of  direct-current  generators,  in  a  general  way  applies  to  direct- 


DYNAMOS,  MOTORS  AND  MOTOR-GENERATORS  31 

current  motors,  as  the  essential  elements  of  one  are  identical  with  those  of  the 
other.  In  the  case  of  a  motor  the  carbon  brushes  resting  on  the  commutator 
serve  to  lead  the  current  from  some  external  source  into  the  coils  of  the 
armature  and  through  the  field  winding,  thus  causing  the  armature  to  rotate, 
and  by  means  of  a  pulley  mounted  on  one  extremity  of  its  shaft,  by  gearing, 
or  by  direct  mechanical  connection  of  the  shaft,  furnishes  mechanical  power 
for  any  desired  purpose.  Similarly  to  dynamos,  motors  are  series  wound, 
shunt  wound  or  compound  wound.  In  a  series  motor  the  field  consists  of  a 
relatively  small  number  of  turns  of  large  wire  directly  connected  in  series 
with  the  line  and  the  armature.  The  current  in  the  armature  coils  and  in  the 
field-magnet  winding  is  of  the  same  value. 

A  shunt-wound  motor  has  field  magnets  wound  with  a  large  number  of 
turns  directly  connected  with  the  brush  terminals  of  the  machine  or  across  the 
terminals  of  the  external  circuit  supplying  the  motor  with  current.  In  the 
case  of  a  shunt  motor  the  strength  of  the  field  current  is  independent  of  the 
current  strength  in  the  armature. 

Compound- wound  motors  may  have  the  two  field  windings  connected  so  as 
to  form  cumulative  winding,  or  differential  winding.  In  the  former  case  the 
magnetizing  effects  of  both  windings  are  in  conjunction,  while  in  the  latter  they 
are  in  opposition.  With  the  cumulative  winding,  increasing  the  load  of  the 
motor  increases  the  magnetic  strength  of  the  field,  while  with  the  differential 
winding  an  increase  of  load  decreases  the  field  strength. 

In  most  towns  and  cities  throughout  the  country  commercial  electric  power 
is  available  for  the  purpose  of  driving  motors.  In  the  majority  of  places  there 
is  but  one  potential  and  one  kind  of  current  at  hand.  In  some  cases  no- volt 
direct  current,  in  others  no-volt  alternating  current  may  be  the  only  power 
available.  In  some  cities  there  is  no  other  choice  but  to  use  200-  or  2 50- volt 
alternating  current,  or  5oo-volt  direct  current. 

It  is  possible  to  obtain  electric  motors  designed  to  operate  with  a  given 
potential  or  character  of  current,  whether  direct  current  or  alternating  current, 
and  as  in  the  operation  of  telegraph  circuits  four  or  five  different  voltages  are 
needed,  all  that  is  required  is  to  have  each  separate  dynamo  mechanically 
connected  with  and  driven  by  a  motor  which  may  be  operated  by  the  available 
commercial  voltage.  Thus  the  various  individual  motors  are  operated  by,  say 
no  volts  direct  current,  or  200  volts  alternating  current,  while  the  individual 
dynamos  driven  by  these  motors  may  have  outputs  ranging  from  40  volts 
to  400  volts,  or  any  other  potentials  for  which  they  may  be  designed. 

In  practice  it  is  best  to  employ  the  lower  voltages  for  the  operation  of  motors 
as  it  is  found  that  when,  for  instance,  500  volts  direct  current  is  used  to  operate 
motors,  heating  and  sparking  difficulties  are  quite  frequent  and  annoying. 
When  there  is  a  choice  between  500  volts  direct  current  and  an  alternating- 
current  potential  of  no  volts  or  220  volts,  it  is  common  practice  to  employ 
an  alternating-current  motor  to  operate  on  the  alternating  current  available, 


32  A  M  ERIC  A  N  TELEGRAPH  PRA  CTICE 

this  motor  in  turn  being  directly  connected  to  a  no- volt  direct-current  dynamo, 
the  latter  furnishing  current  to  operate  the  various  motors  which  drive  the  dyna- 
mos generating  the  various  telegraph  currents.  In  this  way  it  is  possible  to 
get  away  from  the  use  of  the  objectionable  500  volts  direct  current,  and  at  the 
same  time  effect  a  saving  in  primary-current  consumption. 

Also,  it  is  usual  to  arrange  for  "auxiliary"  or  "reserve"  power  to  provide 
against  interruption  to  service  in  case  the  external  source  of  power  fails. 

Where  both  alternating-current  and  direct-current  sources  of  commercial 
power  are  available  it  is  common  practice  to  use  them  alternately,  or  to  use  one 
of  them  regularly  and  maintain  the  other  as  reserve. 

Alternating-current  Motors.1 — There  are  three  types  of  alternating-current 
motor  in  commercial  use,  namely : 

Single-phase  series  type. 
Synchronous  type. 
Induction  motor. 

The  latter  is  the  type  usually  employed  in  telegraph  service  for  the  purpose  of 
driving  small  direct-current  dynamos. 

It  has  been  shown  in  the  case  of  a  direct-current  motor  that  the  armature 
revolves  between  the  pole  faces  of  stationary  field  magnets. 

To  comprehend  the  forces  at  work  in  the  operation  of  an  induction  motor, 
consider  a  direct-current  motor  armature  with  current  traversing  its  coils. 
When  the  field  magnets  are  charged,  the  armature  will  turn ;  but  suppose  the 
brushes  which  rest  on  the  commutator  are  removed  and  the  terminals  of  the 
armature  coils  connected  to  a  copper  ring.  Then,  if  instead  of  the  field  magnets 
remaining  stationary  they  be  revolved  around  the  armature,  it  follows  that  the 
magnetic  lines  will  travel  around  in  a  circle,  at  the  same  time  setting  up  an 
electromotive  force  in  the  armature  coils.  As  these  coils  are  short  circuited 
by  the  copper  ring,  the  current  induced  in  the  armature  coils  sets  up  a  reaction, 
which  results  in  a  drag  which  pulls  the  armature  around  in  a  direction  the  same 
as  that  taken  by  the  rotating  magnetic  field.  In  the  induction  motor,  instead  of 
the  field  magnets  being  revolved  mechanically,  the  magnet  windings  are  so 
connected  with  the  external  circuit  that  the  active  field  moves  around  the  circle 
in  a  given  direction,  thus  causing  the  armature  to  rotate  in  unison  with  the 
constantly  moving  field. 

The  induction  motor  has  two  essential  elements,  the  stator  (Fig.  iga)  and 
the  rotor  (Fig.  igb).  The  stator  consists  of  a  stationary  framework  of  circular 
construction  which  serves  to  support  the  primary  winding,  which  is  connected 
in  the  manner  shown  theoretically  in  Fig.  20.  The  projecting  cores  shown  are  di- 

1  It  has  been  thought  best  not  to  take  up  in  this  work  the  subject  of  the  generation  of 
polyphase  alternating  currents.  While  commercial  alternating  current  is  used  to  operate 
motors  directly  connected  to  direct-current  dynamos  for  telegraph  requirements,  alternat- 
ing currents  are  used  only  in  a  very  li  mi  ted  way  in  the  operation  of  telegraph  lines. 


DYNAMOS,  MOTORS  AND  MOTOR-GENERATORS 


33 


vided  into  groups.  In  the  section  illustrated  the  poles  of  one  group  are  marked 
M,  (xz)  and  (#3),  the  poles  of  a  second  group  (3/1),  (y2)  and  (y3)  and  those  of 
a  third  group  (zi),  (z2)  and  (z3).  It  may  be  observed  that  the  consecutive  poles 


FIG.  iga. — Stator  of  induction  motor. 


FIG.  igb. — Rotor  of  induction  motor. 

of  any  group  are  separated  by  a  number  of  poles  corresponding  to  the  number  of 
groups  employed,  and  that  the  winding  around  each  pole  of  any  group  alternates 
in  direction  from  pole  to  pole,  thus  producing  north  and  south  poles  consecu- 

3 


34 


AMERICAN  TELEGRAPH  PRACTICE 


lively.  If  a  three-phase  alternating  current  be  connected  across  the  terminals, 
the  polarity  of  the' magnet  poles  of  any  group  will  be  reversed  twice  during  each 
cycle,  and  the  active  magnetic  field  progresses  around  the  circle  due  to  the  fact 
that  any  three  poles  located  consecutively  are  magnetized  to  a  maximum  one 
after  another  in  order  around  the  frame.  Thus  is  produced  the  rotating 
magnetic  field. 


FIG.  20. — Stator  magnet  poles  and  winding  connections  of  induction  motor. 

The  Rotor. — The  core  of  the  rotor  is  made  of  laminated  steel  punchings 
mounted  on  an  iron  spider.  Each  slot  in  the  core  contains  a  single  copper  bar 
which  is  made  fast  to  a  short-circuiting  ring  at  either  end  of  the  bars.  The 
e.m.f.  produced  in  the  copper  bars  of  the  rotor  is  very  low,  but  the  force  ex- 
erted upon  the  rotor  by  the  revolving  field  is  such  that  the  induction  motor  is 
quite  efficient  as  a  source  of  power.  Having  no  brushes  or  commutator,  this 
type  of  motor  is  simple  to  operate  and  to  maintain. 

The  Motor-generator. — On  page  31  reference  is  made  to  the  use  of  alter- 
nating-current motors  directly  connected  to  direct-current  dynamos  for  the 
purpose  of  generating  in  the  telegraph  office  no  volts  direct  current  to  be  used 
to  operate  the  various  motors  which  in  turn  are  mechanically  connected  to 
the  dynamos  having  different  voltage  outputs. 

This  type  of  machine  is  known  a?  a  motor-generator,  having  been  given 
this  name  to  distinguish  it  from  the  motor-dynamo  to  be  described  presently. 

One  of  the  standard  makes  of  motor-generators  is  shown  in  Fig.  21. 
The  induction  motor  is  on  the  left,  while  on  the  right  is  shown  the  direct- 
current  generator.  In  making  up  these  units  to  meet  operating  conditions, 
the  motor  may  be  designed  to  operate  on  either  alternating  current  or  direct 


DYNAMOS,  MOTORS  AND  MOTOR-GENERATORS 


35 


current,  and  on  whatever  voltage  is  available,  while  the  generator  end  may  be 
designed  to  produce  any  required  voltage. 

Motor-dynamos. — Motor-dynamos  have  the  two  machines  on  one  base 
directly  connected  by  a  steel  shaft  and  each  machine  has  its  own  field  coils,  see 


FIG.  21. — Motor  generator. 


*  V 


FIG.  22. — Motor  dynamo. 


Fig.  22.     Some  of  these  machines,  notably  the  Crocker- Wheeler  type,  have 

the  two  armature  windings  on  the  same  shaft  but  separated  electrically. 

Another  type  of  machine  known  as  the  dynamotor  is  extensively  used  in 

telegraph  work.     This  machine  has  a  single  field  for  both  motor  and  dynamo 


36 


AMERICAN  TELEGRAPH  PRACTICE 


ends,  see  Fig.  23 .  The  armatures  are  of  the  iron-clad  type  with  slots  or  grooves 
around  the  outside  in  which  the  armature  wires  are  laid  and  held  fast  by  re- 
taining wedges,  readily  removable  when  repairs  are  necessary.  The  armature 
core  consists  of  sheets  of  soft  annealed  steel  punchings.  The  copper  con- 
ductors in  the  armature  are  insulated  with  mica  strips  or  with  oiled  muslin 
and  fibrous  materials.  Regulation  of  the  voltage  of  the  dynamo  is  accom- 
plished by  varying  the  speed  of  the  motor  by  means  of  a  controlling  rheostat. 
Both  in  the  motor-dynamo  and  the  dynamotor  each  end  of  the  machine — 
that  is,  the  motor  end  and  the  dynamo  end — have  their  own  commutator  and 
brushes.  The  capacity  of  a  double  field  motor-dynamo  is  determined  by  the 
capacity  of  the  motor  end  and,  since  the  dynamo  operation  is  independent  of 
the  motor,  all  the  methods  of  control  practised  with  dynamos  may  be  used  in 


FIG.  23. — Dynamotor. 


these  machines  without  affecting  the  motor.  The  dynamo  field  may  have  a 
shunt  winding  or  a  compound  winding  to  insure  constant  pressure  regardless 
of  variations  in  load..  In  single  field  dynamotors,  the  motor  and  dynamo  ar- 
matures are  combined  in  one,  thus  requiring  a  single  field  only;  that  is,  the  pri- 
mary armature  winding  in  association  with  the  common  field  which  operates 
as  a  motor  to  drive  the  machine,  and  the  secondary  or  dynamo  winding  which 
operates  as  a  generator  to  produce  the  secondary  current  are  upon  the  same 
armature  core.  The  armature  reaction  of  one  winding  neutralizes  that  of 
the  other  and  saves  energy  required  for  magnetizing  the  fields. 

Dynamotors  can  stand  a  somewhat  greater  overload  than  motor-dynamos 
but  their  e.m.f .  drop  cannot  be  compensated  by  compound  winding,  as  in  the 
case  of  the  motor-dynamo.  Also,  since  both  windings  of  dynamotors 
are  on  the  same  core  and  under  the  influence  of  a  single  field  the  ratio  of  trans- 
formation cannot  be  varied  or  adjusted.  Any  regulation  of  the  field  strength 


DYNAMOS,  MOTORS  AND  MOTOR-GENERATORS 


37 


will  simply  make  the  machine  run  faster  or  slower,  as  the  ratio  of  the  turns  of 
wire  on  the  dynamo  end  of  the  armature  to  those  on  the  motor  end  is  un- 
changeable. The  voltage  of  the  dynamo  end  must,  therefore,  remain  in  the 
same  ratio  as  the  voltage  on  the  motor  end.  The  voltage  of  a  single  machine 
may  be  regulated  by  using  a  rheostat  in  series  with  the  motor  armature  for 
reducing  its  speed;  but  this  wastes  energy  as  much  as  when  resistances  are 
used  to  cut  down  the  secondary  voltage  and  interferes  with  the  constant  speed 
of  the  machine  to  the  disad- 
vantage of  the  regulation  of 
the  dynamotor  for  constant 
pressure. 

Figure  24  shows  a  view  of  a 
dynamotor  armature,  with  the 
motor  commutator  on  one  end 
of  the  shaft,  the  dynamo  arma- 
ture on  the  opposite  end,  and 
the  windings  of  each  in  the 
center. 

Motor  Current  Regulation. 
—When  an  electric  motor  is  at 

rest  and  the  switch  controlling  the  supply-current  circuit  is  closed  in  the  act  of 
starting  the  motor,  the  initial  rush  of  current  through  the  low-resistance  arma- 
ture coils  is  excessive  unless  a  protective  resistance  is  placed  in  series  with  the 
supply  mains.  In  order  to  limit  the  amount  of  current  permitted  to  traverse 
the  armature  conductors,  a  rheostat  or  starting  box  is  used.  When  a  motor  is 
started,  a  reaction  takes  place  in  the  armature  which  produces  a  counter- 
electromotive  force,  due  to  the  action  of  the  inductors  in  the  armature  cutting 
through  the  magnetic  lines  of  force  produced  at  the  field  magnet  poles.  The 
counter-e.m.f.  developed  opposes  in  direction  that  of  the  supply  e.m.f.,  thereby 
in  a  sense  automatically  controlling  the  current  volume  in  the  armature 
windings. 


FIG.  24. — Dynamotor  armature. 


By  employing  Ohm's  law  (/  =  ^)  for  the  purpose,  the  amount  of  current 
in  the  armature  may  be  determined,  thus : 

Where  /  is  the  current  in  the  armature, 

E  the  impressed  e.m.f.  (supply  voltage), 
R  the  resistance  of  the  armature, 

Then: 


Therefore,  to  reduce  the  current  volume  in  the  armature  coils  at  the  instant 


38 


AMERICAN  TELEGRAPH  PRACTICE 


of  starting  the  motor,  additional  resistance  must  be  inserted  in  the  circuit,  and 
with  given  factors  we  have : 

7-r 


R+Ri 

Where  /    is  the  current  in  the  armature, 
E  the  impressed  e.m.f., 
Ex  the  counter  e.m.f., 
R  the  armature  resistance, 
R!  the  resistance  of  the  starting  box. 


FIG.  25. — Two-pole  shunt  motor-starting  rheostat  connections. 

The  starting  resistance  in  the  rheostat  is  gradually  reduced  until  all  is  cut  out. 
The  counter-electromotive  force  of  a  motor  builds  up  as  the  speed  of  the 
armature  increases  in  the  same  way  as  the  voltage  of  a  dynamo  increases  with 
increase  of  speed;  therefore,  as  the  starting-box  resistance  is  gradually  cut  out, 
the  counter-e.m.f.  increases  to  its  maximum,  reaching  that  value  when  the  full 
voltage  from  the  supply  mains  is  impressed  on  the  motor  terminals. 


DYNAMOS,  MOTORS  AND  MOTOR-GENERATORS  39 

Figure  25  shows  the  wiring  and  connections  of  a  2 -pole  shunt  motor  with 
starting  box  inserted.  The  connections  shown  are  the  same  as  those  used  in 
wiring  the  motor  end  of  dynamo  tor  sets,  motor-dynamo  sets,  and  motor- 
generator  sets,  where  direct-current  motors  are  used. 

An  important  feature  of  the  starting  box  is  the  electromagnet  shown  on 
the  right  of  the  drawing  and  at  the  end  of  the  row  of  resistance  contact  disks. 
This  magnet  serves  to  hold  the  rheostat  arm  in  the  "running"  position  as  long 
as  the  magnet  coil  is  energized  by  current  from  the  supply  mains.  Should  the 
supply  circuit  be  interrupted  the  magnet  coil  is  demagnetized,  and,  due  to  the 
force  of  gravity,  the  arm  drops,  thus  breaking  the  main-line  contact  at  C.1 

It  is  evident  that  the  automatic-release  feature  of  the  starting  box  protects 
the  motor  armature  from  the  injurious  effects  of  sudden  rushes  of  full  line  volt- 
age when  the  supply  circuit  is  restored.  A  momentary  interruption  to  the 
supply  circuit  does  not  cause  the  automatic  release  to  operate  as,  due  to 
momentum,  the  motor  armature  continues  to  run  a  short  time  after  the  supply 
current  is  shut  off  and  generates  an  e.m.f.,  which  furnishes  current  for  the  fields 
and  the  cut-off  magnet. 

Starting  Boxes. — The  resistance  of  the  starting  rheostat  to  be  used  in  con- 
nection with  a  motor  depends  upon  the  amount  of  current  required  to  start  the 
motor,  at  full-load.  The  resistance  should  be  of  sufficient  capacity  to  safely 
carry  the  current  indicated  by  the  normal  rating  of  the  motor. 

The  word  rheostat  is  derived  from  greek  pstu,  to  flow,  and  err  arcs,  fixed. 
A  device  for  regulating  the  flow  of  current. 

In  those  cases  where  it  is  necessary  continuously  to  use  additional  resistance 
in  the  armature  circuit  of  direct-current  motors  for  the  purpose  of  controlling 
the  speed,  the  rheostat  coils  must  have  large  current-carrying  capacity  and  the 
construction  of  the  rheostat  must  be  such  that  it  will  have  ample  radiating 
surface  in  order,  as  far  as  possible,  to  avoid  excessive  heating. 

Most  modern  rheostats  have  the  resistance  wire  wound  on  hollow  asbestos, 
clay  or  porcelain  bobbins,  each  bobbin  after  being  wound  with  the  desired 
amount  of  resistance  wire  is  entirely  covered  with  an  insulating  enamel  which 
protects  the  unit  against  mechanical  injury  and  prevents  short-circuiting  of 
turns.  The  various  resistance  units  are  assembled  to  form  a  complete  rheostat. 
In  case  a  unit  becomes  defective,  it  may  be  replaced  without  disturbing  the 
remaining  units. 

Figure  26  shows  the  wiring  of  a  commercial  type  of  starting  box  much  used 
in  telegraph  work.  It  may  be  seen  that  the  connection  between  each  resist- 
ance unit  is  brought  out  to  a  contact  disk.  The  contacts  are  arranged  in  the 
arc  of  a  circle,  so  that  the  rheostat  arm  pivoted  at  the  center  may  make  a  sliding 
contact  with  the  connections,  cutting  in  or  out  the  amount  of  resistance  required 
for  regulation  of  speed.  In  using  a  starting  box  in  connection  with  a  shunt- 

1  In  some  types  of  starting  boxes  the  rheostat  arm  is  withdrawn  from  the  deenergized 
magnet  through  the  action  of  a  spring  attached  to  the  arm. 


40 


AMERICAN  TELEGRAPH  PRACTICE 


wound  or  compound-wound  motor,  the  first  contact  to  which  the  arm  is  moved 
places  all  of  the  resistance  in  series  with  the  armature  and  the  series  field  wind- 
ing, and  each  successive  step  cuts  out  a  portion  of  the  resistance  until  the  arm 
is  moved  into  contact  with  the  disk  on  the  extreme  right,  when  all  of  the  resist- 
ance is  cut  out  and  the  rheostat  is  said  to  be  "set"  in  the  running  position. 

It  should  be  borne  in  mind  that  starting  resistances  are  designed  and 
intended  for  momentary  use  only,  and  the  rheostat  arm  should  never  be  stopped 
on  any  intermediate  step  longer  than  a  second  or  two,  as  the  excessive  heating 
of  the  coils  is  likely  to  cause  burn-outs. 


FIG.  26. — Connections  and  wiring  of  motor-starting  rheostat. 

The  total  resistance  of  motor  starting  boxes  usually  is  such  that  when  the 
rheostat  arm  is  moved  to  the  first  contact,  one  and  one-half  times  the  full 
torque  current  of  the  motor  will  flow  through  the  armature  winding.  To  start 
a  motor  from  a  position  of  rest  and  accelerate  it  to  full  speed  within  a  reasonably 
short  time  requires  one  and  one-half  times  the  full  torque  current  of  the  motor 
at  full-load.  Although  the  duration  of  this  excess  of  current  is  brief,  it  is 
necessary  to  protect  the  armature  by  employing  a  device  which  will  open  the 
motor  circuit  when  a  current  50  per  cent,  above  its  normal  rating  is  permitted 
to  flow  for  more  than  a  fraction  of  a  minute. 

An  enclosed  fuse  is  generally  employed  for  the  purpose.  In  a  given  case,  for 
instance,  a  fuse  may  be  employed  which  has  been  designed  to  "open"  when  a 
current  50  per  cent,  above  its  rated  capacity  flows  through  it  during  30  seconds 
time.  If  the  fuse  employed  is  of  the  2o-ampere  class,  a  current  of  30  amperes 
flowing  through  it  for  a  period  of  30  seconds  would  cause  a  temperature  rise 
in  the  fuse  wire  which  would  melt  it  and  thus  open  the  circuit  of  which  the  fuse 
forms  a  part. 

Fuses  in  Motor  Circuits. — The  necessity  for  employing  starting  resistance 


DYNAMOS,  MOTORS  AND  MOTOR-GENERATORS  41 

in  motor  circuits  is  apparent  from  the  knowledge  that  the  resistance  of  the  arma- 
ture winding  is  very  low,  about  0.4  ohm.  In  cases  where  no- volt  supply 
current  is  used  to  operate  the  motor,  if  no  starting  resistance  were  inserted, 
theoretically,  there  would  be  a  current  of  275  amperes  in  the  armature  at  the 
instant  the  main  switch  is  closed.  This  would  cause  destructive  sparking  and 
possibly  melt  the  soldered  connections. 

When  a  starting  resistance  is  employed,  and  gradually  cut  out  by  means  of 
the  rheostat  arm  as  the  motor  armature  accelerates  and  generates  an  opposing 
e.m.f.,  the  disastrous  effects  of  excessive  initial  current  are^  avoided.  In  view 
of  the  above,  the  necessity  for  careful  handling  of  the  starting  resistance  is 
apparent. 

In  order  to  provide  against  mishap  to  the  starting  resistance  or  to  the  motor 
— overload — it  is  customary  to  "fuse"  the  motor  circuit  so  that  a  current  large 
enough  to  cause  heating  of  the  conductors  or  connections  will  not  be  permitted 
to  exist  long  enough  to  do  damage. 

The  cartridge  type  of  enclosed  fuse  (the  form  approved  by  the  fire  under- 
writers) consists  of  a  short  length  of  wire  made  of  lead  in  combination  with  a 
certain  percentage  of  tin.  Tin  fuses  (melts)  at  a  temperature  of  235°  C.,  and 
lead  at  325°  C.  In  making  fuse  wire  a  squirting  process  is  employed,  similar 
to  that  used  in  making  incandescent  lamp  filaments.  The  fuse  wire  is  packed 
in  an  asbestos  wrapping  and  enclosed  in  a  pasteboard  tube  equipped  with  brass 
thimbles  at  either  end,  each  end  of  the  fuse  wire  being  soldered  to  one  of  the 
thimbles. 

Fuse  blocks  are  equipped  with  spring  brass  clips  set  a  sufficient  distance 
apart  to  accommodate  a  particular  length  of  fuse;  this  construction  is  quite 
convenient  for  quickly  replacing  defective  fuses. 

Motor  circuits  are  fused  on  both  sides,  otherwise,  one  side  becoming 
grounded  at  one  point  and  the  other  side  at  another  point,  a  circuit  might  be 
established  with  no  fuse  in  action. 

Overload  Motor- starters. — The  overload  attachment  to  a  motor-starter 
consists  of  a  magnet  the  coils  of  which  carry  the  total  current  consumed  by 
the  motor.  When  the  current  becomes  excessive,  the  magnet  attracts  its 
armature  and  completes  a  short  circuit  around  the  terminals  of  the  retaining 
magnet  which  holds  the  rheostat  arm  at  the  "full  on"  position.  The  short 
circuit  is  closed  by  means  of  two  brass  posts  conveniently  mounted  on  the  face 
of  the  starter.  The  holding  magnet  is  thus  demagnetized,  the  rheostat  arm 
flies  back  to  the  "off"  position,  inserting  the  total  resistance  of  the  starter, 
opens  the  circuit  and  stops  the  motor. 

Underload  Release. — Diagram  26  shows  the  wiring  of  a  standard  type  of 
starting  box  including  a  no-voltage  release  attachment. 

A  type  of  "remote-control"  motor-starter  used  in  telegraph  work  is  illus- 
trated in  the  photographic  reproduction,  Fig.  27. 

In  the  larger  telegraph  centers  it  is  necessary  to  have  a  number  of  5o-volt 


42 


AMERICAN  TELEGRAPH  PRACTICE 


and  loo-volt  potentials  available  for  intermediate  battery  purposes.  For, 
while  ordinarily  the  regular  battery  arrangements  are  sufficient  to  take  care 
of  circuit  requirements,  there  are  occasions  when,  temporarily  at  least,  addi- 
tional battery  is  required  to  maintain  currents  of  a  requisite  strength  to  satis- 
factorily operate  lines. 

Inasmuch  as  these  extra  battery  facilities  are  for  emergency  service  and  are 
used  only  for  short  periods  during  the  day,  a  switching  arrangement  is  provided 
whereby  the  switchboard  attendants  in  the  main  operating-room  may,  at  will, 
start  and  stop  any  one  or  all  of  the  machines  intended  for  intermediate  battery 
purposes,  even  though  the  machines  are  located  in  a  part  of  the  building  remote 
from  the  operating-room. 


FIG.  27. — Solenoid  motor-starter. 

Figure  270  shows  the  connections  of  the  automatic  starter  used  for  this 
purpose.  The  motor  supply  mains  are  connected  to  the  switch  sw  which 
regularly  is  left  closed.  The  coils  C  are  solenoids  having  double  windings, 
which  when  energized  pull  up  the  plungers  P.  To  the  lower  extremity  of  each 
plunger  is  attached  metal  or  carbon  contact  plates  P\  which  act  as  a  switch  to 
open  or  close  the  armature  and  field  circuits  of  the  motor  in  response  to  the 
operation  of  the  plungers.  If  the  circuits  are  traced  it  may  be  noted  that  the 
resistance  coil  5  remains  in  series  with  the  armature  for  a  short  time  after  the 
motor  circuit  is  closed,  and  is  short-circuited  only  after  the  armature  has 
speeded  up  sufficiently  to  avoid  the  effects  of  the  initial  inrush  of  current. 
Four  wires  are  shown  leading  from  the  engine-room,  or  dynamo-room  to  the 
operating-room  switchboard,  where  they  terminate  in  a  specially  constructed 
double-contact  pin-jack. 


DYNAMOS,  MOTORS  AND  MOTOR-GENERATORS 


43 


The  insertion  of  a  double-conductor  plug  in  the  jack  closes  both  the  motor 
and  dynamo  circuits.  The  "wedge"  end  of  the  connecting  cord  is  inserted 
in  series  with  the  line  at  the  spring-jack  as  shown  on  the  right. 

Alternating-current  Motor-starters. — Alternating-current  motors  take  a 
large  current  when  started  under 
load,  so  large  in  fact  that  unless 
proper  provision  is  made  against 
it,  serious  fluctuation  of  line  vol- 
tage occurs  when  any  motor  on 
the  circuit  is  started-up.  To  avoid 
this  a  means  is  employed  whereby 
a  reduced  voltage  is  applied  to  the 
motor  at  starting,  this  is  gradually 
increased  until  the  full-line  voltage 
is  applied  to  the  motor  terminals 
when  the  rotor  has  reached  full 
speed. 

The  usual  type  of  controller 
employed  is  called  an  auto-starter, 
which  consists  of  a  specially  de- 
signed switching  system,  operat- 
ing in  conjunction  with  two  auto- 
transformers.  The  transformers 
are  in  circuit  with  the  supply  mains. 
Each  transformer  consists  of  a 
winding  from  which  a  series  of  taps 
are  made,  each  tap  providing  for 
a  different  voltage.  As  these  taps 
are  successively  connected  with 
the  motor  by  means  of  the  switch 
an  increasing  voltage  value  is  ap- 
plied to  the  motor  terminals  until 
finally  the  full  line-voltage  is  thrown 
on.  The  losses  due  to  transform- 
ing continue  only  during  the  start- 
ing process  because  when  the 
full  line-voltage  is  applied  the  auto- 
transformers  are  disconnected 

from  the  circuit.  In  moving  the  auto-starter  handle  from  one  notch  to  the 
next  the  circuit  is  for  an  instant  entirely  interrupted.  Under  ordinary  con- 
ditions breaking  and  making  the  circuit  would  cause  violent  sparking,  the  con- 
tacts, however,  are  made  and  broken  in  a  chamber  filled  with  oil,  thus 
materially  reducing  the  liability  of  sparking. 


FIG.  270. — Connections  and  wiring  of  solenoid 
motor-starter. 


44 


AMERICAN  TELEGRAPH  PRACTICE 

Supply 


a                                  b                                    c  d 

FIG.    28a. — Four-      FIG.  286.— Three-      FIG.    280.— Four-  FIG.  28^.— Three- 

wire    two-phase     wir  e  two-phase     wire,   two-phase  wire,    two-phase 

motor  connections.       motor  connections,     motor  connected  motor      connected 

through   an    auto-  through    an   auto- 
transformer,  transformer. 


To  Line 


Two-Phase  Motor 
Auto-Starter  in  Starting  Position 


Three- Phase  Motor 
Auto-Starter  in  Starting  Position 


FIG.  29. 


FIG.  30. 


,n 


Off  Position 


Starting  Positions 

\    f\   j      Running  Position 


FIG.  31, 


FIGS.  29,  30,  31,  32. 


FIG.  32. 


DYNAMOS,  MOTORS  AND  MOTOR-GENERATORS 


45 


Figure  280  shows  the  connections  of  a  two-phase  squirrel-cage  motor; 
the  wires  a  and  b  belong  to  one  phase  and  the  wires  c  and  d  to  the  other.  In 
some  instances  the  two  wires  belonging  to  one  phase  are  marked  a  and  the 
two  wires  of  the  other  phase  marked  b,  but  in  general  any  two  wires  which 
are  found  to  have  voltage  between  them  belong  to  one  phase  or  the  other. 
Fig.  2 8b  shows  the  connections  of  a  three- wire  two-phase  system,  the  wire  b 
or  " common  return"  being  connected 
jointly  to  the  two  center  terminals. 
Fig.  2$>c  shows  a  two-phase  four- wire 
motor  connected  through  an  auto-trans- 
former. Fig.  2%d  shows  a  two-phase 
three-wire  system  connected  through  an 
auto-transformer. 

After  a  four-wire  two-phase  motor 
has  been  connected  up,  should  it  develop 
that  rotation  is  in  a  direction  the  reverse 
of  that  desired  all  that  is  necessary  is  to 
interchange  the  two  wires  of  one  phase; 
that  is  a  and  b}  or  c  and  d. 

Figure  29  shows  the  connections  of  a 
two-phase  motor  and  auto-starter. 

Figure  30  shows  the  connections  of  a 
three-phase  motor  and  auto-starter. 

Figure  31  shows  the  connections  and 
internal  wiring  of  a  four-wire  two-phase 
auto-starter  of  the  oil-immersed  type. 
The  motor  terminal  markings  are  shown 
on  the  right,  namely,  Ai,  A2,  Bi,  82. 

Figure  32  shows  a  view  of  the  auto- 
starter  complete  with  the  handle  in  the 
"off"  position,  while  the  starting  and 
running  positions  are  shown  in  dotted  lines. 

Dynamo  Current  Regulation. — The  output  of  dynamos  may  be  controlled 
by  regulating  the  speed  of  the  dynamo  armature,  or  by  regulating  the  current 
strength  in  the  field  winding  of  the  dynamo. 

When  motor-generators  or  motor-dynamos  are  employed,  the  first-named 
method  may  be  availed  of  by  inserting  a  field  regulating  rheostat  in  the  field 
circuit  of  the  motor  as  explained  in  connection  with  Figs.  23  and  24.  Regula- 
tion of  voltage  through  control  of  the  field  strength  of  the  generator  is  accom- 
plished by  inserting  a  rheostat  as  shown  in  Fig.  13,  which  shows  the  internal 
wiring  and  terminal  connections  of  a  shunt- wound  2 -pole  generator. 

The  connections  of  a  compound- wound  2-pole  dynamo  are  shown  in  Fig.  33. 


FIG.  33. — Complete  wiring  connections 
of  a  two-pole  compound  dynamo. 


CHAPTER  IV 


STORAGE  BATTERIES 

CURRENT  RECTIFIERS;  MERCURY-ARC  AND  ELECTROLYTIC 

The  names  storage  battery,  secondary  cell,  and  accumulator  have  been 
given  to  that  type  of  battery  which  consists  of  elements  capable  of  absorbing 
electrical  energy  and  storing  it  in  the  form  of  chemical  energy. 

The  type  of  storage  cell  most  generally  employed  in  telegraph  work  con- 
sists of  a  number  of  lead  plates  immersed  in  a  dilute  solution  of  sulphuric  acid. 
Alternate  plates  of  a  cell  are  joined  together  making  up  the  positive  element; 
the  balance  of  the  plates  similarly  joined  constitute  the  negative  element. 
See  Figs.  34,  340  and  346. 


FIG.  34.  FIG.  340. 

FIGS.  34,  340,  346. — Storage  cells. 


FIG.  346. 


The  negative  plate  consists  of  a  lead  grid  in  the  interstices  of  which  is 
fixed  a  litharge  paste  consisting  of  sulphuric  acid  and  oxide  of  lead,  this,  in 
forming,  changes  to  metallic  gray  lead.  The  positive  plate  of  red  lead  in 
forming  changes  to  peroxide  of  lead.  The  electrolytic  solution  is  made  up 
of  i  part  sulphuric  acid  (H2SO4)  and  5  parts  distilled,  or  rain  water. 

Externally  the  direction  of  current  is  from  peroxide  of  lead  plate  through 
the  connecting  circuit  and  back  to  the  negative,  or  lead  "sponge"  plate. 
This  is  the  condition  when  the  cell  is  discharging.  Internally,  or  when  the 
cell  is  being  charged  from  an  external  source  of  e.m.f.  the  current  is  in  the 
reverse  direction. 

There  are  several  methods  of  charging  storage  batteries,  and  the  method 
employed  in  a  given  installation  is  dependent  upon  local  conditions,  as  re- 
gards available  sources  of  charging  current.  In  many  instances  it  is  econom- 
ical to  use  the  existing  no- volt  lighting  current  for  the  purpose.  Where 

46 


STORAGE  BATTERIES  47 

commercial  or  private  lighting  circuits  are  not  at  hand,  a  gas-engine-driven 
electric  generator  may  be  used  to  charge  the  cells.  In  considering  the  in- 
stallation of  a  storage  battery  plant,  the  first  thing  to  be  determined  is  the 
desired  output  or  capacity  of  the  plant.  Obviously,  this  depends  upon 
the  number  of  lines  and  circuits  to  be  fed  and  the  amount  of  current  in  am- 
peres, or  fractions  thereof,  required  to  operate  such  circuits.  If,  for  instance, 
there  were  10  wires  to  feed,  each  requiring  40  m.a.  current,  the  10  wires 
would  require  0.4  ampere,  and  if  the  wires  were  to  be  operated  24  hours  per 
day,  the  required  ampere-hours  per  day  would  be 

0.4X24  =  9.6  ampere-hours  per  day. 

This  would  be  the  maximum  demand  made  upon  the  battery,  as  the  above 
calculation  is  based  on  the  possibility  of  the  circuits  being  closed  all  of  the 
time.  In  practice  it  is  found  that,  considering  the  average  of  a  large  number 
of  lines,  circuits  are  closed  a  little  less  than  half  the  time. 

Two  types  of  storage  cell  in  common  use  are  the  "couple"  type,  and  the 
"  multiple  "  type.  In  the  couple  cell  there  are  but  two  plates.  The  multiple 
cell  has  three  or  more  plates.  The  terminals  of  the  plates  in  multiple  cells 
are  either  burned  together  or  bolted  with  lead-covered  bolts. 

Storage  battery  plates  are  made  up  in  several  sizes  which  are  considered 
standard. 

Type  "  E "  plates  are  7  3/4  in.  X  7  3/4  in.  =60  sq.  in. 
Type  "F"  plates  are  10  1/2  in.  Xio  1/2  in.  =no  sq.  in. 
Type  "G"  plates  are  15  1/2  in.  Xi5  1/2  in.  =240  sq.  in. 

The  normal  charging  rate  of  the  "E,"  "F,"  and  "G"  types  of  cell  is  ap- 
proximately 0.08  ampere  per  square  inch  of  positive  plate.  Thus  to  find  the 
normal  charging  rate  of  a  type  "G"  cell  having  6  positive  plates  and  7 
negative  plates,  calculate  as  follows: 

6X240X0.08  =  115.20  amperes. 

When  no- volt  lighting  mains  are  used  to  charge  storage  cells  a  suitable 
number  of  incandescent  lamps  should  be  inserted  in  the  lighting  circuit,  as 
shown  in  Fig.  35,  in  order  to  take  from  the  circuit  a  current  sufficient  to 
charge  the  battery.  An  automatic  bre^k  switch  is  inserted  in  the  circuit 
so  that  in  case  the  primary  current  is  interrupted  the  charging  circuit  will 
be  opened  and  the  storage  battery  prevented  from  discharging  back  through 
the  charging  mains.  The  connections  of  this  switch  are  such  that  an 
electromagnet  energized  by  current  from  the  charging  mains  actuates 
an  armature  which  when  the  current  is  flowing  acts  as  a  switch  to 
keep  the  circuit  closed.  When  the  charging  circuit  is  interrupted,  the 
electromagnet  is  deenergized,  thus  releasing  the  armature  and  opening  the 
circuit.  There  are  several  different  types  of  automatic  switch  which  may 
be  used  for  the  purpose.  One  device  in  common  use  operates  in  the 
reverse  way  to  that  just  described,  that  is,  the  armature  mounted  above 


48 


AMERICAN  TELEGRAPH  PRACTICE 


the  magnet  core  is  adjusted  to  remain  "open"  when  normal  current 
traverses  the  winding  of  the  magnet,  while  the  increment  of  current  due 
to  short  circuit,  attracts  the  armature  and  opens  the  circuit. 

When  a  cell  has  been  fully  charged  the  active  agent  in  the  positive 
plate  consists  of  lead  peroxide,  and  the  negative  plate  has  been  converted 
into  "spongy  lead."  During  the  time  a  storage  cell  is  being  discharged  the 
active  material  in  both  positive  and  negative  plates  is  being  converted  into 
"lead  sulphate,"  due  to  the  extraction  of  the  sulphion  from  the  acid  of 
the  electrolyte.  After  discharge,  when  a  cell  is  recharged,  the  positive 


Line 


Line 


Lamps 


ferfMUUta 
CWpiufa*. 

TottKirfk- 

ratuaLupi 

BT 

CT 

PT 

ET 

1-9 

110 

1-16  c  p. 

8-16  c  P. 

3-32  c.  P. 

5-32  c.  P. 

10-18 

110 

1  82  c.  p. 

2-32  c.  p. 

4-32  c.  P. 

6-32  C.  p. 

19-27 

110 

1-82  c.  P. 

5-16  c.  P. 

5-32  c.  P 

7-32  C  P. 

28-33 

110 

2-32  c  P. 

4-32  c.  p. 

8-32  c.  p. 

U-32C.P. 

60-60 

1-16  c.  P. 

2-16  c  P. 

4-16  c.  P. 

6-16  c.  P. 

Load 


FIGS.  35,  36. — Storage  battery  "charging"  and  " discharging  "circuits. 

plate  is  converted  back  into  lead  peroxide,  and  the  negative  plate  into 
spongy  lead.  It  is  only  the  material  of  which  the  .buttons  are  made  that 
undergoes  chemical  changes,  as  the  supporting  grid,  consisting  of  a  lead- 
antimony  combination  is  acted  upon  only  in  a  small  degree.  A  peculiarity 
of  lead  (due  to  the  formation  of  a  coating  of  sulphate)  is  that  it  is  insoluble 
in  sulphuric  acid. 

The  statement  above  made,  to  the  effect  that  during  discharge  the  active 
material  in  both  positive  and  negative  plates  is  converted  into  lead  sulphate, 
is  based  on  the  latest  and  most  generally  accepted  theory  of  the  action  that 
takes  place. 

Figures  35  and  36  show  the  connections  of  storage  battery  charging  and 
discharging  circuits  as  usually  arranged. 

INSTALLATION  AND  MANAGEMENT  OF  STORAGE  CELLS 

Location  of  Battery. — The  proper  location  of  the  battery  is  important. 
It  should  preferably  be  in  a  separate  enclosure  or  compartment,  which  should 
be  well  ventilated,  dry  and  of  moderate  temperature. 


STORAGE  BATTERIES  49 

The  ventilation  should  be  free,  not  only  to  insure  dryness,  but  to  prevent 
chance  of  an  explosion,  as  the  gases  given  off  during  charge  form  an  explosive 
mixture  if  confined.  For  this  reason  never  bring  an  exposed  flame  near  the 
battery  when  it  is  gassing. 

To  obtain  the  best  results,  the  temperature  should  be  between  50°  and  80° 
F.  If  the  temperature  is  very  high,  that  is,  over  80°  F.,  for  any  great  length 
of  time,  the  wear  on  the  plates  is  excessive.  If  the  temperature  is  low,  no 
harm  results,  but  the  available  capacity  is  reduced  during  the  period  of  low 
temperature. 

Installing  Battery. — Place  the  jars,  after  they  have  been  cleaned,  in  posi- 
tion on  the  sand  trays,  which  should  previously  be  filled  evenly  with  the  top 
with  fine  dry  bar  sand.  The  trays,  which  should  be  separated  by  an  air  gap, 
rest  on  glass  insulators,  which  in  turn  rest  on  stands  or  shelves.  The  cells 
should  be  so  located  in  the  room  that  they  will  be  easily  accessible  and  if 
practicable  should  be  in  one  tier;  where  two  or  more  tiers  are  necessary,  ample 
head  room  over  each  tier  should  be  allowed  for.  If  sand  trays  are  not  pro- 
vided, the  jars  may  rest  directly  on  a  board  or  plank,  in  sections  of  not  more 
than  10  cells  each,  the  plank  being  insulated  from  the  stand  or  shelf  by  glass 
insulators,  and  an  air  gap  left  between  the  section  rests. 

Plates  of  opposite  polarity,  except  the  terminal  plates,  are  burned  to- 
gether by  a  connecting  strap,  forming  a  "couple, "  and  are  placed  in  adjoining 
jars;  the  positive  plates  are  of  a  brownish  color,  the  negatives  of  a  light  gray. 
Before  placing  the  couples  in  the  jars,  the  straps  should  be  bent  over  a  piece  of 
wood  3/4  inch  thick,  the  top  edge  of  which  is  rounded.  After  removing  from 
the  form,  the  straps  should  be  still  further  bent  until  the  lower  edges  of  the 
plates  touch;  then  by  gently  springing  them  apart  when  putting  into  the  jars 
the  plates  of  adjacent  couples  will  not  have  a  tendency  to  get  together  and 
short  circuit.  In  bending,  care  should  be  taken  that  only  the  connecting  strap 
is  bent,  as  the  burned  joints  must  not  be  subjected  to  undue  strain.  The 
plates  must  be  placed  in  the  jars,  so  that  in  each  there  will  be  both  a  positive 
and  a  negative  plate  and  the  sections  of  the  battery  must  be  connected,  pref- 
erably by  lead  tape,  so  that  the  positive  and  negative  terminals,  which  are 
the  single  plates,  will  be  connected  a  positive  and  negative  together  in  each 
case.  If  couples  or  sections  are  installed  in  the  wrong  direction,  the  plates 
will  be  seriously  injured.  Rubber  separators  are  used  only  in  Type  "BT" 
cells;  in  other  types  no  separators  at  all  are  used. 

Connecting  up  the  Charging  Circuit. — Direct  current  only  must  be  used 
for  charging.  If  alternating  current  alone  is  available,  a  current  rectifier 
must  be  used  for  obtaining  direct  current.  Before  putting  the  electrolyte  into 
the  cells  the  circuits  connecting  the  battery  with  the  charging  source  must  be 
complete,  care  being  taken  to  have  the  positive  pole  of  the  charging  source 
connected  with  the  positive  end  of  the  battery,  and  the  negative  pole  with  the 
negative  end  of  the  battery.  If  a  suitable  voltmeter  is  not  at  hand,  the  polar- 


50  AMERICAN  TELEGRAPH  PRACTICE 

ity  may  be  determined  by  dipping  two  wires  from  the  charging  terminals  into 
a  glass  of  water  to  which  a  teaspoonful  of  table  salt  has  been  added,  care  being 
taken  to  keep  the  ends  at  least  i  in.  apart  to  avoid  danger  of  short  circuits. 
Fine  bubbles  of  gar,  will  be  given  off  from  the  negative  pole. 

Electrolyte. — The  electrolyte  used  for  filling  new  cells  is  dilute  sulphuric 
acid  of  a  specific  gravity  of  1.180  or  22°  Baume  (except  Type  "ET,"  see  note), 
as  shown  on  the  hydrometer  at  a  temperature  of  70°  F.  When  new  electro- 
lyte is  required  it  can  be  made  by  mixing  pure  sulphuric  acid  (1.840  sp.  gr.,  or 
66°  Baume)  and  distilled  water  in  the  proportion  of  i  part  acid  to  5  1/4  of 
water,  by  volume,  for  1.180  sp.  gr.  When  mixing,  pour  the  acid  slowly  into 
the  water  (not  the  water  into  the  acid)  and  thoroughly  stir  with  a  wooden 
paddle.  The  final  specific  gravity  must  be  read  when  the  solution  is  cool. 
A  metal  vessel  must  not  be  used  for  mixing  or  handling  the  solution;  a  glazed 
earthenware  crock  or  a  lead  lined  tank  is  suitable,  or  a  wooden  vessel  which  has 
not  been  used  for  any  other  purpose,  such  as  a  new  wash  tub,  can  be  used  for 
mixing,  but  not  for  storing,  the  electrolyte.  The  electrolyte  must  be  cool 
when  poured  into  the  cells. 

NOTE. — For  Type  "ET"  cells,  when  being  first  put  into  commision,  electrolyte  of  1.210 
sp.  gr.,  or  25°  Baume  must  be  used.  If  the  electrolyte  is  to  be  mixed  on  the  ground,  the 
proportions  of  acid  (of  1.840  sp.  gr.,  or  66°  Baume)  and  water  are  i  part  acid  to  4  1/2  of 
water  (by  volume). 

With  the  battery  properly  installed  and  the  charging  connections  made 
ready,  the  electrolyte  can  be  poured  into  the  cells,  filling  until  the  plates  are 
covered  1/2  in. 

Initial  Charge. — The  charge  should  be  started  at  the  normal  rate  (see 
"  Table  of  Ratings,")  as  soon  as  the  electrolyte  is  in  the  cells  and  continued  at 
the  same  rate,  provided  the  temperature  of  the  electrolyte  is  well  below  100° 
F.,  until  there  is  no  further  rise  or  increase  in  either  the  voltage  or  specific 
gravity  and  gas  is  being  freely  given  off  from  all  the  plates.  Also,  the 
color  of  the  positive  plates  should  be  a  dark  brown  or  chocolate,  and 
the  negatives  a  light  slate  or  gray.  The  temperature  of  the  electro- 
lyte should  be  closely  watched,  and  if  it  approaches  100°  F.  the  charg- 
ing rate  must  be  reduced  or  the  charge  stopped  entirely  until  the  tem- 
perature stops  rising.  From  30  to  40  hours  at  the  normal  rate  will  be 
required  to  complete  the  charge;  but  if  the  rate  is  less,  the  time  must  be  pro- 
portionately increased.  The  specific  gravity  will  fall  somewhat  after  the 
electrolyte  is  added  to  the  cells,  and  will  then  gradually  rise  as  the  charge 
progresses,  until  it  is  up  to  1.210,  or  thereabouts.  The  voltage  for  each  cell 
at  the  end  of  the  charge  will  be  between  2.5  and  2.7  volts,  and  for  this  reason 
a  fixed  or  definite  voltage  should  not  be  aimed  for.  It  is  of  the  utmost  im- 
portance that  the  initial' charge  should  be  complete  in  every  respect.  If  there 
is -any  doubt,  it  is  better  to  charge  too  long  than  risk  injury  to  plates  by  stop- 
ping the  initial  charge  before  it  is  complete. 


STORAGE  BATTERIES  51 

After  the  completion  of  a  charge  (initial  or  with  the  battery  in  regular  ser- 
vice) and  the  current  off,  the  voltage  will  quite  rapidly  fall  to  about  2.05  volts 
per  cell  and  there  remain  while  on  open  circuit,  falling  to  2  volts  when  the 
discharge  is  started. 

Operation;  Battery  in  Service. — Excessive  charging  must  be  avoided,  nor 
must  a  battery  be  undercharged,  overdischarged  or  allowed  to  stand  com- 
pletely discharged. 

The  battery  should  be  preferably  charged  at  the  normal  rate.  It  is  im- 
portant that  it  should  be  sufficiently  charged,  but  the  charge  should  not  be 
continued  beyond  that  point.  Both  from  the  standpoint  of  efficiency  and 
life  of  the  plates,  the  best  practice  is  the  method  which  embraces  what  may 
be  called  a  regular  charge,  to  be  given  when  the  battery  is  from  one-half  to 
two-thirds  discharged,  and  an  overcharge  to  be  given  weekly  if  it  is  necessary 
to  charge  daily,  or  once  every  two  weeks  if  the  regular  charge  is  not  given 
so  often. 

The  regular  charge  (at  or  as  near  normal  rate  as  possible)  should  be  con- 
tinued until  the  voltage  across  the  battery  has  risen  to  a  point  which  is  0.05 
to  o.  i o  volts  per  cell  below  what  it  was  on  the  preceding  overcharge,  the  charg- 
ing rate  being  the  same  in  both  cases;  for  instance,  if  the  maximum  voltage  per 
cell  attained  on  the  overcharge  is  2.52,  the  voltage  per  cell  to  be  reached  on 
the  regular  charge  is  fyrom  2.42  to  2.47  volts  per  cell.  In  cases  where  it  is 
possible  to  accurately  determine  the  amount  of  discharge  in  ampere-hours, 
the  following  method  is  permissible  and  may  be  found  more  suitable,  partic- 
ularly where  there  is  difficulty  in  reading  the  voltmeter  closely:  charge  at  the 
normal  rate  until  the  number  of  ampere-hours  charged  exceeds  the  preceding 
discharge  by  from  5  to  15  per  cent. 

The  overcharge  (at  the  same  rate  as  regular  charge)  should  be  continued 
until  the  voltage  across  the  battery  has  been  at  a  maximum  for  one  hour,  five 
successive  i5-minute  readings  showing  no  further  rise  and  all  cells  are  gassing 
freely.  If  rate  is  less  than  normal,  the  time  at  maximum  must  be  propor- 
tionately increased. 

On  discharge  the  voltage  should  not  be  allowed  to  fall  below  1.75  volts  per 
cell,  with  current  at  normal  rate;  the  limiting  voltage,  however,  is  higher 
if  the  rate  is  less  than  normal,  and  lower  if  the  rate  is  more  than  normal. 

Inspection. — Once  every  two  weeks,  on  the  day  before  the  overcharge,  a 
specific-gravity  reading1  of  all  cells  should  be  taken,  and  likewise  all  cells 
should  be  carefully  examined  to  see  that  the  plates  are  not  touching  each  other 
or  otherwise  short  circuited  and  have  normal  color.  Near  the  end  of  the  over- 
charge all  cells  should  be  looked  over  to  see  that  they  are  gassing  freely. 

Low  Cells;  Indications  and  Treatment. — Falling  off  in  specific  gravity  or 
voltage  relative  to  the  rest  of  the  cells.  Lack  or  deficiency  of  gassing  on 

1  On  Type  "BT"  cells  an  individual  cell- voltage  reading,  taken  just  before  the  end  of 
overcharge,  may  be  substituted  for  the  specific-gravity  reading,  taking,  however,  a  gravity 
reading  at  least  once  every  three  months. 


52  AMERICAN  TELEGRAPH  PRACTICE 

overcharge  as  compared  with  surrounding  cells.  Color  of  plates  markedly 
lighter  or  darker  than  the  surrounding  cells. 

In  case  of  any  of  the  above  symptoms  being  noted,  inspect  the  cell  care- 
fully for  the  cause  and  remove  at  once.  Short  circuits  are  to  be  removed  with 
a  thin  strip  of  hard  rubber  or  wood;  never  use  metal. 

If,  after  the  cause  of  the  trouble  has  been  removed,  the  readings  do  not 
come  up  at  the  end  of  overcharge,  the  battery  as  a  whole,  or  preferably  the 
section  in  which  the  low  cell  is  located,  should  receive  a  separate  or  extra 
charge. 

Impurities  in  the  electrolyte  will  also  cause  a  cell  to  work  irregularly. 
Should  it  be  known  that  any  impurity  has  gotten  into  a  cell,'  it  should  be  re- 
moved at  once.  In  case  removal  is  delayed  and  any  considerable  amount  of 
foreign  matter  becomes  dissolved  in  the  electrolyte,  this  solution  should  be 
replaced  immediately,  thoroughly  flushing  the  cell  with  water  and  putting  in 
new  electrolyte  of  1.210  sp.  gr. 

Sediment. — The  accumulation  of  sediment  in  the  bottom  of  the  jars  must 
be  watched  and  not  allowed  to  touch  the  plates,  as,  if  this  occurs,  rapid  de- 
terioration will  result.  To  remove  the  sediment,  the  simplest  method  is  to 
lift  the  couples  out  of  the  jars  after  the  battery  has  been  fully  charged,  draw 
or  pour  off  the  electrolyte,  clean  out  the  jars  and  get  the  couples  back  and 
covered  with  electrolyte  again  as  quickly  as  possible,  so  that  there  will  be  no 
chance  of  the  plates  drying  out.  Some  new  electrolyte  (1.210  sp.  gr.)  will 
be  required  to  replace  that  lost.  When  work  is  completed  charge  until  volt- 
age has  been  at  maximum  for  five  hours  and  adjust  gravity  to  standard. 

Evaporation. — Do  not  allow  the  surface  of  the  electrolyte  to  get  down  to 
the  top  of  the  plates;  keep  it  at  its  proper  level  (1/2  in.  above  the  top  of  the 
plates)  by  the  addition  of  pure  water  only,  which  should  be  added  at  the  be- 
ginning of  a  charge,  preferably  the  overcharge.  To  transport  or  store  the 
water,  use  clean,  covered  glass  or  earthenware  vessels. 

Restoring  Lowered  Specific  Gravity. — It  will  not  be  necessary  to  add 
new  electrolyte,  except  at  long  intervals  (once  every  year  or  two),  or  when 
cleaning.  When  the  specific  gravity,  with  the  cells  in  good  condition  and 
at  full  charge  and  normal  temperature  (70°  F.),  has  fallen  to  1.190,  it 
should  be  restored  to  standard  (1.205  to  1.215)  by  the  addition  of  new  elec- 
trolyte instead  of  water  when  replacing  evaporation.  To  correct  to  normal 
temperature,  subtract  one  point  (o.ooi  sp.  gr.)  for  each  3°  F.  below  70°  and  add 
one  point  for  each  3°  F.  above  70°;  for  instance,  electrolyte  which  is  1.213  at 
61°  and  1.207  at  79°  will  be  1.210  at  70°. 

Battery  used  but  occasionally;  Putting  the  battery  out  of  commission  and 
in  again. — If  the  battery  is  to  be  used  at  infrequent  periods,  then  a  refreshing 
charge  should  be  given  once  every  two  weeks.  If  the  use  of  the  battery  or  any 
of  its  cells  is  to  be  discontinued  for  a  considerable  time,  then  it  must  be  treated 
as  follows :  After  thoroughly  charging,  siphon  or  pour  off  the  electrolyte  (which 


STORAGE  BATTERIES 


53 


may  be  used  again)  into  thoroughly  cleaned  carboys  or  other  glass  receptacles 
which  can  be  covered  to  keep  out  impurities,  and  as  each  cell  becomes  empty, 
immediately  fill  it  with  fresh,  pure  water.  When  water  is  in  all  the  cells,  allow 
the  battery  to  stand  12  or  15  hours;  and  then  draw  off  the  water  and  the  battery 
can  then  be  allowed  to  stand  without  further  attention.  To  put  into  service 
again,  proceed  as  in  the  case  of  the  initial  charge;  but  use  for  all  types,  either 
new  electrolyte  of  1.210  sp.  gr.,  or  if  the  old  electrolyte  has  been  saved,  add 
enough  new  of  1.210  sp.  gr.  to  replace  loss.  If  the  gravity  after  the  first  charge 
is  low,  it  should  be  restored  to  standard. 

Obtaining  Additional  Life. — When  the  condition  of  the  battery  as  a  whole 
is  such  that,  due  to  normal  wear  on  the  plates,  it  will  not  do  its  regular  work, 
considerable  additional  life  can  be  obtained  from  the  plates  by  removing  the 
couples  from  the  jars  and  bending  the  connecting  strap  in  the  reverse  direction, 
so  that  the  sides  of  the  plate  which  were  against  the  jar  will  face  each  other  in 
the  same  cell;  in  other  words,  the  insides  of  the  plates  become  the  outsides. 

TABLE  OF    RATINGS 


Type 

LT 

BT 

CT 

PT 

ET 

Size  of  plates                          .  . 

Sf'Xs" 

7f"X7f" 

Normal  rate  (amperes)  charge 
and  discharge. 

J 

1 

it 

3 

41 

THE  EDISON  NICKEL-IRON  STORAGE  CELL 

While  on  the  subject  of  storage  batteries,  it  may  be  well  to  give  a  brief 
description  of  the  Edison  nickel-iron  storage  cell  recently  brought  out,  and 
which  is  the  latest  development  in  this  country  in  the  manufacture  of  secondary 
cells.  So  far,  the  new  Edison  battery  has  been  employed  chiefly  in  operating 
the  motors  of  electric  vehicles,  but  inasmuch  as  its  construction  is  a  new  depar- 
ture in  storage-battery  engineering  and  as  its  performance  has  been  quite 
satisfactory,  its  possibilities  as  an  efficient  and  economical  source  of  e.m.f. 
may  in  the  course  of  time  insure  it  a  more  extended  use  commercially.  The 
latest  type  of  the  Edison  cell  is  known  as  "type  A."  Two  sizes  of  cell,  known 
as  A~4  and  A-6,  have  four  and  six  positive  plates  respectively.  Instead  of 
employing  a  lead-peroxide  and  acid-electrolyte  combination  as  is  usual  in  the 
construction  of  lead  storage  cells,  the  Edison  cell  employs  active  materials  con- 
sisting of  nickel  and  iron  oxides  for  the  positive  and  negative  electrodes,  in 
combination  with  an  alkaline  electrolyte,  the  latter  being  a  solution  of  caustic 
potash  in  water.  The  retaining  vessels  are  made  of  sheet  steel,  all  seams  being 


54  AMERICAN  TELEGRAPH  PRACTICE 

welded  by  the  autogenous  method.  The  retaining-cans  are  electroplated  with 
nickel,  which  protects  the  steel  from  rust. 

A  type  A~4  cell  contains  four  positive  and  five  negative  plates.  Each 
positive  plate  consists  of  a  grid  of  nickelplated  steel  supporting  the  active  mate- 
rial which  is  contained  in  two  rows  of  tubes,  15  in  each  row.  The  tubes  are 
made  from  thin  sheet  steel,  perforated  and  nickelplated,  each  tube  being  rein- 
forced by  eight  ferrules  which  preserve  correct  alignment  and  prevent  expansion 
of  the  tubes.  The  active  material  in  the  tubes  is  intermixed  with  thin  flakes 
of  pure  metallic  nickel  which  are  produced  by  an  electrochemical  process. 
The  negative  element  or  plate  consists  of  24  rectangular  pockets  supported  in 
a  nickelplated  steel  grid,  in  three  horizontal  rows.  These  pockets  are  the  same 
as  the  tubes  in  the  positive  element  except  in  shape  and  dimension.  Each 
pocket  is  filled  with  oxide  of  iron  or  iron  rust.  When  the  pockets  have  been 
assembled  in  the  negative  grid,  the  whole  is  subjected  to  a  heavy  pressure  which 
produces  a  solid  and  compact  unit.  The  plates  are  assembled  in  the  container 
in  a  manner  similar  to  that  employed  in  assembling  lead  cells.  The  electrolyte 
consists  of  a  2 1  per  cent,  solution  of  caustic  potash  in  distilled  water. 

It  is  claimed  that  the  Edison  cell  does  not  deteriorate  when  left  uncharged 
and  that  it  is  not  injured  by  overcharging. 

CURRENT  RECTIFIERS 

The  Mercury-arc  Rectifier. — Current  from  an  alternating-current  source 
may  be  changed  to  direct  current  by  means  of  current  rectifiers.  The  diagram, 
Fig.  37,  shows  theoretically,  the  connections  of  the  " mercury"  rectifier. 
The  alternating  current  to  be  rectified  is  supplied  through  the  transformer 
shown  at  the  top  of  the  diagram. 

When  a  current  of  electricity  is  made  to  flow  in  a  given  direction  between 
two  points  in  a  circuit  separated  by  a  gap  containing  vapor  of  mercury,  should 
the  direction  of  current  be  changed  suddenly,  the  current  will  be  interrupted 
due  to  a  peculiar  characteristic  of  mercury  which  in  effect  opposes  a  change  in 
direction  of  current. 

Referring  to  Fig.  37,  £  represents  a  glass  tube  or  globe  containing  a  deposit 
of  mercury  and  exhausted  of  air.  Terminals  A,  A',  B  and  C  are  sealed  in  the 
glass.  If  at  a  given  instant  the  terminal  X  of  the  alternating-current  supply 
circuit  is  positive,  the  terminal  A  is  then  positive  and  the  arc  will  flow  between 
the  terminal  A  and  the  mercury  terminal  J5,  continuing  on  through  the  storage 
battery  F,  through  reactance  coil  DI  and  back  to  negative  terminal  Y  of  the 
transformer.  An  instant  later  when  the  impressed  e.m.f.  has  dropped  to  a 
value  insufficient  to  maintain  the  arc  against  the  counter-e.m.f.  of  the  arc  and 
the  load,  the  reactance  coil  DI  which  has  been  charging  now  produces  an  induc- 
tive discharge  in  the  same  direction  as  formerly,  which  assists  in  maintaining 
the  arc  until  the  e.m.f.  of  the  supply  circuit  has  passed  through  zero;  reversed, 
and  built  up  in  the  opposite  direction  sufficiently  to  strike  an  arc  between  A' 


CURRENT  RECTIFIERS 


55 


and  the  mercury  terminal  B.  The  arc  now  being  maintained  between  A '  and  B 
is  supplied  with  the  combined  current  from  the  transformer  and  from  the  coil 
DI.  Obviously  the  current  in  the  alternating-current  supply  circuit  is  con- 
stantly changing  in  direction,  thus  tending  to  enter  at  A  and  leave  at  A',  and 
in  the  reverse  direction  to  enter  at  A '  and  leave  at  A  a  great  number  of  times 
per  second.  The  only  action,  however,  which  can  take  place  is  that  the  first 
impulse  enters  at  A'  and  leaves  at  B  and,  due  to  the  maintenance  of  the  arc 
as  before  explained,  the  next  impulse  will  enter  at  A  and  leave  at  B.  Therefore 
the  current  continuously  flows  out  at  B  in  the  same  direction  (direct  current). 
The  choke  coils  D  and  DI  obstruct  alternating  , 

current,   but   permit   direct    current    to    pass      ' VVWWWVWV ' 

through.  Were  it  not  for  the  action  of  these 
coils  a  current  wave  coming  down  either  side 
would  divide  and  be  neutralized. 

Electrolytic  Rectifiers. — One  type  of  elec- 
trolytic rectifier  (the  "Hickley")  consists  of  a 
solution  or  electrolyte,  such  as  phosphate  of 
soda,  in  combination  with  carbon  and  aluminum 
electrodes,  contained  in  a  vessel  F,  Fig.  38,  to 
which  are  attached  radiator  loops  R  permitting 
circulation  of  the  solution  (necessary  on  account 
of  heat  developed  in  the  cell)  thereby  prevent- 
ing the  weakening  of  the  electrolyte.  The 
direct  current  supplied  by  the  rectifier  is,  of 
course,  pulsating,  but  owing  to  the  condenser 
effect  of  the  cells  whereby  a  portion  of  the 
current  is  recovered,  currents  are  derived  which 
are  sufficiently  steady  for  telegraph  require- 
ments. With  this  type  of  rectifier  80  volts 
direct  current  are  procurable  from  no  volts  al- 
ternating-current primary  voltage.  The  durability  of  the  electrolyte  and  the 
electrodes  of  this  rectifier  depends  upon  the  amount  of  energy  delivered,  but 
if  not  overworked  the  rectifier  will  not  require  renewal  oftener  than  once  each 
year,  assuming  daily  operation.  A  suitable  transformer  T  is  utilized  to  give 
either  higher  or  lower  voltage  than  that  supplied  by  the  available  alternating- 
current  .mains,  the  rectifier  being  designed  to  supply  e.m.fs.,  ranging  from  6  to 
1,000  volts.  These  rectifiers  may  be  operated  on  any  alternating-current  fre- 
quency from  25  to  133  cycles. 

The  electrolytic  rectifier  is  based  purely  upon  the  principles  of  electrolytic 
action  as  utilized  in  various  branches  of  the  electrical  arts. 

If  two  rods  of  aluminum  are  placed  in  a  vessel  containing  an  alkaline 
solution  such  as  carbonate  of  soda  or  phosphate  of  soda,  and  an  attempt  is 
made  to  pass  a  current  of  electricity  from  one  rod  to  the  other  through  the 


FIG.  37. — Mercury-arc  current 
rectifier. 


56 


AMERICAN  TELEGRAPH  PRACTICE 


solution,  it  is  found  that  during  a  brief  interval  current  will  flow  and  then 
entirely  cease.  If,  however,  one  of  the  aluminum  rods  is  replaced  by  a  rod 
of  carbon,  iron,  or  platinum,  it  at  once  develops  that  current  will  flow  from  the 
carbon  to  the  aluminum  electrode,  but  not  in  the  reverse  direction.  The 
reason  is  given  that  the  carbon  gives  off  a  gas  which 
is  dissipated  through  the  electrolyte,  while  the 
aluminum  electrode  (if  positive)  retains  a  portion1  of 
the  gases  generated.  These  gases,  hydrogen  and 
oxygen,  unite  with  minute  portions  of  the  aluminum 
and  form  hydroxide  of  aluminum.  The  aluminum 
electrode  being  coated  with  hydroxide  prevents  the 
flow  of  current  from  it;  therefore,  when  an  alternat- 
ing current  is  supplied  to  the  two  electrodes  it  is 
only  when  the  current  is  positive  to  the  -carbon 
that  current  flows.  It  is  evident  that  the  negative 
impulse  is  obliterated,  and  that  the  secondary  cur- 
rent delivered  through  the  rectifier  will  consist  of  the 
succeeding  positive  impulses  only.  With  an  alter- 
nating current  of  low  frequency  it  would  seem  that 
the  utilization  of  alternate  impulses  only  would 
produce  a  secondary  current  so  slowly  pulsating 
that  it  would  not  be  sufficiently  continuous  for 
practical  requirements,  but  the  condenser  effect 
above  referred  to  operates  to  tide  over  the  no-cur- 
rent intervals,  and  in  practice  it  is  found  that  the 
rectified  currents  are  quite  satisfactory  as  direct 
currents. 

MANAGEMENT  OF  THE  ELECTROLYTIC  RECTIFIER 

±          The  Solution. — The  solution  used  in  the  Hickley 

-„  -,-,,    ,    ,  f.  rectifier   is   non-inflammable  and  does  not  contain 

.TIG.  3°- — Jiiieciroiy tic  rec- 
tifier and  switch  panel.       &Cld. 

In  setting  up  the  solution  distilled  water  or  rain 
water  free  from  foreign  matter  and  acids  should  invariably  be  used. 

Evaporation  and  decomposition  of  the  water  of  the  solution  should  be 
taken  care  of  by  occasionally  adding  fresh  water.  The  amount  of  water 
decomposed  is  proportional  to  the  amount  of  current  in  watts  passing 
through  the  solution. 

When  the  solution  has  become  "milky"  in  appearance  and  there  is  de- 
posited a  sediment  in  the  bottom  of  the  cell,  the  solution  requires  renewing. 
xThe  sediment  deposited  contains  small  particles  of  aluminum  which  act  as 
conductors  and,  consequently,  reduce  the  efficiency  of  the  cell. 


CURRENT  RECTIFIERS 


57 


The  Electrodes. — The  aluminum  electrodes  are  made  of  a  special  alloy 
and  are  fitted  with  glazed  porcelain  tops.  The  formation  of  the  hydroxide  of 
aluminum  takes  from  the  electrode  minute  particles  of  aluminum,  so  that 
the  greater  the  demand  for  current  made  upon  the  rectifier,  the  greater  is  the 
disintegration  that  takes  place.  The  porcelain  cap  should  be  kept  secure  and 
tight,  else  the  solution  will  creep  under  it  and  interfere  with  proper  rectification, 
and  allow  the  electrode  and  the  solution  to  become  quite  hot.  Electrodes 
should  be  suspended  freely  in  the  center  of  the  jar  and  should  not  be  per- 
mitted to  touch  the  sides.  The  electrodes  should  not  be  handled  any  more 
than  is  absolutely  necessary,  as  the  hydroxide  is 
liable  to  be  destroyed  by*  undue  handling. 

Installing  and  Starting. — The  location  of  the 
rectifier  should  be  a  place  where  there  is  good  air 
circulation.  The  cells  should  be  supported  on  in- 
sulators as  it  i?  important  that  there  should  be  no 
electrical  contact  between  the  rectifier  and  the 
ground,  or  between  tlje  cells.  Owing  to  the  possi- 
bility of  the  hydroxide  coating  being  destroyed 
in  shipping,  it  is  well  in  setting  up  new  cells  to  take 
the  precaution  to  pass  a  small  current  through 
the  rectifier  for  an  hour  or  so  before  the  entire  load 
is  thrown  on.  Should  a  rectifier  for  any  reason  be 
retired  for  an  indefinite  period,  it  is  well  to  remove 
the  electrodes  and  hang  them  in  a  dry  place  where 
they  will  be  free  from  handling  until  required  for 
service.  If  inspection  of  the  rectifier  should  dis- 
close cracks  in  the  porcelain  cap  of  an  electrode, 
the  electrode  should  be  replaced  immediately. 

The  humming  sound  sometimes  in  evidence  may 
be  due  to  the  operation  of  the  transformer  or  the 
reactance,  but  should  the  sound  increase  in  volume, 
it  is  probable  that  a  defect  has  developed  and  that 

alternating  current  is  passing  through.  The  gases  released  by  decomposi- 
tion of  the  water  in  the  solution  escape  through  vent  holes  in  the  top  of 
the  cells.  After  long  continued  operation  it  may  be  found  that  the  gases 
have  carried  upward  particles  of  the  chemicals  from  the  solution,  which  on 
coming  in  contact  with  the  air  have  formed  crystals  in  and  around  the  vent 
holes,  thus  interfering  with  the  escape  of  the  gases.  Vent  holes  should  be 
kept  free  of  obstructions.  Crystals  which  may  have  formed  should  be 
brushed  back  into  the  cell,  where  they  will  quickly  dissolve.  Fig.  39  is  a 
reproduction  of  a  photograph  of  a  type  B  Hickley  rectifier. 


FIG.    39. — Electrolytic  rec- 
tifier and  switch  panel. 


CHAPTER  V 

POWER-BOARD  WIRING;  BATTERY  SWITCHING  SYSTEMS  AND 

ACCESSORIES 

It  is  desirable  that  currents  furnished  by  dynamos  for  the  operation  of 
telegraph  circuits  should  be  as  nearly  continuous  as  possible.  By  this  is 
meant  that  the  currents  so  supplied  should  closely  resemble  the  non-pulsatory 
currents  derived  from  primary  batteries.  The  internal  resistance  of  the 
gravity  battery  is  about  21/2  ohms  per  cell,  and  this  resistance  in  itself  has 
the  effect  of  controlling  the  current  derived  from  a  given  number  of  cells. 
For  instance,  suppose  a  certain  battery  consists  of  100  cells,  each  cell  having 
an  internal  resistance  of  2  1/2  ohms,  and  an  e.m.f.  of  1.07  volts;  by  Ohm's  law 
it  may  be  shown  that  on  short  circuit  the  current  available  from  the  battery 
will  be  0142  ampere,  or  about  420  milliamperes,  for 

100 

0.42  ampere. 


2.5    Xioo 

Machine  generators  of  electricity,  such  as  are  employed  to  furnish  telegraph 
currents,  have  a  very  low  internal  resistance;  considerably  less  than  an  ohm. 
When  these  machines  are  employed  in  place  of  chemical  batteries,  it  is  custom- 
ary to  insert  in  the  potential  leads  a  total  resistance  which  equals  about  2  ohms 
per  volt  in  order  to  protect  the  generators  in  case  short  circuits  occur  in  the 
telegraph  apparatus,  or  in  event  of  grounds  occurring  on  line  wires  at  points 
close  to  the  home  office,  and  also  for  the  purpose  of  controlling  excessive 
"  sparking"  between  the  contact  points  of  instruments,  where  circuits  carrying 
comparatively  large  currents  are  opened  and  closed  continuously.  l 

The  purpose  of  the  power-board  is  to  provide  convenient  mounting  for 
the  various  accessories  which  as  a  whole  make  up  the  battery  switching  system. 

In  most  installations  the  power-board  has  mounted  upon  it  the  switches 
and  fuses  controlling  the  primary  or  motor  circuits  as  well  as  those  controlling 
the  secondary  or  dynamo  circuits.  Other  accessories  usually  mounted  on 
the  face  of  the  board  include  ammeters,  voltmeters,  and  field-regulating 
rheostats. 

When  the  type  of  battery  resistance  unit  employed  consists  of  a  coil  of 

1  As  explained  in  a  later  chapter,  the  present  tendency  of  American  telegraph  engineer- 
ing in  this  regard,  is  to  reduce  the  amount  of  resistance  inserted  in  the  potential  leads.  A 
reduction  of  the  number  of  ohms  per  volt  of  potential  requires  that  dependence  must  be 
placed  in  fuses  to  protect  the  dynamo  in  the  event  of  short  circuits,  and  that  improved 
means  must  be  availed  of  to  reduce  the  spark  at  "make"  and  "break"  contacts, 

58 


POWER-BOARD  WIRING 


59 


"resistance"  wire  the  various  units  are  mounted  on  "coil  racks,"  and  when 
the  type  of  resistance  used  consists  of  a  form  of  incandescent  lamp,  the  resist- 
ance units  are  mounted  in  "banks."  Dynamo  leads  go  directly  from  the 
power-board  to  the  coil  racks,  or  to  the  lamp  banks,  as  the  case  may  be. 

The  diagram,  Fig.  40,  shows  the  motor  "supply"  wires  leading  from  the 
busbars,  through  the  fuses  in  each  side  of  the  circuit,  to  a  double-pole  single- 
throw  knife  switch,  the  latter  serving  to  close  or  open  the  circuit  leading  to 
the  motor  end  of  a  dynamotor.  The  dynamo  end  is  shown  as  having  the 
negative  terminal  grounded.  The  positive  terminal  is  connected  through  the 
power-board  and  "resistance"  rack  to  its  prearranged  service  assignment 
in  the  operating-room. 


To  Power  Board 
thence    < 


fuses 


/D.P.SJ.  Switch 


Field 


fo  Coil  Rack  and 
Operating  Room.  Brush 

Dynamo  End 

Brush  TT^ 


Armature 


Brush 

MotorEnd 

Brush 


FIG.  40. — Dynamotor  wiring  connections. 

The  Postal  Telegraph-Cable  Company's  dynamo  arrangement  provides 
that  4o-volt  potentials  supply  current  for  the  operation  of  sounder  circuits, 
repeater  locals,  duplex  and  quadruplex  pole-changer  and  transmitter  key 
circuits,  lamp  annunciator  circuits,  etc.  For  the  operation  of  Morse  short 
single  circuits,  loops,  and  for  intermediate  battery  purposes  85-volt  potentials 
are  employed,  while  the  longer  main-line  wires  operated  single  Morse,  are  fed 
from  i3o-volt  or  2oo-volt  potentials.  Machines  supplying  respectively  200 
volts  of  each  polarity  (positive  and  negative)  are  allotted  to  duplex  operation. 
Three  hundred  and  eighty-five  volts,  positive  and  negative,  respectively,  are 
used  for  the  operation  of  quadruplex  circuits,  and  high-potential  "leak" 
duplex  circuits. 

Forty- volt  mains  for  use  in  local  circuits  are  brought  from  the  coil  racks, 
before  mentioned,  to  fuse-blocks  situated  on  the  tops  of  instrument  tables 


60 


AMERICAN  TELEGRAPH  PRACTICE 


in  the  operating-room.  Forty- volt,  85-volt,  and  i25-volt  mains  for  application 
to  single  main  lines  are  brought  from  coil  racks  to  disks  in  the  main-line  switch- 
board (see  Fig.  41)  and  properly  marked,  indicating  potential  and  polarity. 
Two-hundred-volt  and  385-volt  "plus"  and  "minus"  leads  are  brought 
directly  from  the  power-board  to  cabinets  located  in  the  aisle  ends  of  instrument 
tables,  there  connected  through  the  proper  resistance  coils  to  six-point  switches 
situated  on  the  tops  of  the  tables. 

Figure  42  shows  the  wiring  and  battery  connections  of  the  type  of  six- 
point  switch  used  for  the  purpose.  Throwing  the  switch  lever  to  the  right 
places  the  lower  or  200- volt  potentials  in  connection  with  the  "line"  contacts 


f 

r 

\         / 

~\ 

A: 

/Switcht 

f  ••; 

Resistance* 
Coils-* 

\  \ 

+ 

\  \ 

M 

r 

r- 
r 

"] 

] 

2 

v^^^/ 

ii 

o 

>*—-^ 

^ 

wot 

O 

I 

0 

0 

K5t 

o 

) 

o 

o 

'«•-- 

"•'Fuses  * 

~~> 

85+ 

0 

f 

0 

( 

o 

40+ 

o 

1 

o 

o 

200+ 

J25+ 

^5+ 

AO+ 

L 

Ond 

j 

0 

11 

o. 

IL 

^f 

/      ^    4 

u 

FIG.  41. — Potential  mains  connected  to  battery  disks  in  main  line  switchboard. 

of  the  multiplex  apparatus,  while  throwing  the  lever  to  the  left  connects  the 
higher,  or  3 85-volt  potentials  with  the  line  instruments. 

In  the  newer  offices  the  plan  has  been  followed  of  carrying  all  battery 
wires  leading  from  the  power-board  to  the  main  switchboard  and  to  instrument 
tables,  in  2-in.  iron  piping.  Where  practicable  the  piping  is  imbedded  in 
concrete  flooring  in  the  operating-room.  Cast-iron  hand-holes  made  from 
standard  patterns  are  located  at  the  aisle  end  of  each  table,  the  top  of  the 
hand-hole  extending  up  into  the  wiring  cabinet  built  into  the  end  of  the  table. 
In  this  cabinet  the  various  resistance  coils  and  fuses  are  located. 

The  Western  Union  Telegraph  Company's  dynamo  arrangement  differs 


POWER-BOARD  WIRING  61 

only  in  detail  from  that  just  described.  Owing  to  varying  conditions  in 
different  localities,  uniform  battery  arrangement  has  not  always  been  possible. 
In  some  of  the  older  Western  Union  installations,  the  arrangement  referred  to 
in  the  beginning  of  Chapter  III  is  used,  whereby  a  number  of  dynamos  capable 
of  generating  like  e.m.fs.  are  connected  in  series,  each  machine  having  a  poten- 
tial of,  say,  60  volts.  Six  dynamos,  each  having  an  e.m.f.  of  60  volts,  if  con- 
nected in  series  have  an  aggregate  e.m.f.  of  360  volts.  A  "tap"  taken 
from  the  first  machine  of  the  series  gives  60  volts,  from  the  second  120 


FIG.  42. — Six-point  battery-switch  for  mounting  upon  operating  tables. 

volts,  and  so  on  in  multiples  of  60  volts  until  at  the  end  terminal  of  the  sixth 
machine  an  e.m.f.  of  360  volts  is  available.  As  mentioned  in  Chapter 
III,  with  this  arrangement  it  is  necessary  to  provide  a  series  of  dynamos  for 
each  polarity,  and  to  have  available  a  third  series  as  spare.  In  some  installa- 
tions multiples  of  70  volts  have  been  used  in  arranging  a  series  of  dynamos, 
and  it  is,  of  course,  feasible  to  connect  machines  having  different  voltage  out- 
puts in  a  series,  in  order  to  meet  particular  requirements.  The  chief  objection 
to  the  "series"  arrangement  is  that  in  case  an  individual  machine  of  a  series 
becomes  disabled,  the  entire  series  of  which  it  forms  a  part  has  to  be  shut 
down  until  the  disabled  machine  is  repaired  or  replaced. 


62 


AMERICAN  TELEGRAPH  PRACTICE 


THREE -WIRE  SYSTEM 

Where  conditions  are  such  that  a  three-wire  system  of  commercial  power 
may  be  availed  of  to  advantage,  it  is  possible  by  means  of  power-board  switch- 
ing arrangements  to  obtain  potentials  of  different  values  and  of  both  polarities. 


110) 


220 


FIG.  43. — Three- wire  system. 


no*at  fir  t 
L  OCAL  ANO  f*UL  T/PL.CX  W/R/NG  fffOM  3  W/fff  I/O  VOL.  TMA/NS 


FIG.  44. 

Fig.  43  shows  diagrammatically  the  connections  whereby  two  no- volt  gener- 
ators are  coupled  together  in  some  commercial  power  systems,  for  the  purpose 
of  avoiding  the  stringing  of  an  out-going  and  a  return  conductor  for  each  no- 
volt  generator.  When  two  generators  are  coupled  as  indicated  in  the  diagram, 


POWER-BOARD  WIRING 


63 


one  return  wire  serves  for  both  machines.  Also  there  is  the  additional  advan- 
tage that  while  each  generator  external  circuit  is  separate,  for  all  practical  pur- 
poses, it  is  possible  to  obtain  from  the  two  outside  wires  a  potential  of  220  volts 
— no  positive  and  no  negative. 

Figure  44  gives  the  connections  usually  made  when  the  three- wire  system  is 
utilized  for  telegraphic  purposes.  By  following  the  connections  it  may  be  seen 
that  either  the  no- volt  positive  or  negative  wire  may  be  applied  direct  to 
quadruplex  locals,  main  lines  or  call  circuits,  by  way  of  the  single-pole 
double-throw  switch,  i/2-ampere  fuses  and  regulation  resistance  coils;  the 
latter  mounted  on  coil  racks  previously  referred  to,  while  the  fuses  and  the 
knife  switch  are  mounted  on  the  face  of  the  power  board. 


COILS  aOO~0/tM3  CACH 


CO/L  BOAffO 


SOOSrsf?  W/f?/NG  fOrt QUADRUPLE* 
f/fOAf  TH/f££  W//?£/f0  VOL  TM/l/t/S. 


FIG.  45- 

By  connecting  the  two  outside  conductors  of  the  three-wire  service  through 
the  double-pole  single-throw  switch,  fuses,  and  resistance  coils,  no-volt 
potential  is  obtained  for  the  operation  of  duplex  circuits;  that  is,  no  volts  of 
each  polarity. 

The  double-pole  single-throw  switch  also  places  the  commercial  no-volt 
positive  and  negative  leads,  each  in  series  with  the  generator  terminals  of 
"booster"  motor-generators,  thereby  adding  the  voltage  of  the  latter  to 
that  of  the  former.  Boosters  having  out-puts  of  130  volts  positive  and 
negative  respectively  and  connected  as  shown  in  Fig.  44,  raise  the  potentials 
to  240  volts  for  the  operation  of  duplexes  and  short  quadruplexes. 


64 


AMERICAN  TELEGRAPH  PRACTICE 


BOOSTER  CONNECTIONS 


Figure  45  shows  the  starting-box  and  "booster"1  connections  necessary  to 
obtain  quadruplex  potentials  of  each  polarity  from  three- wire  mains. 


Generator  Pole  Changing 
Switch  for  Meter. 


A.C.  Motor 
No.  2 


FIG.  46. — Typical  power-board  wiring. 

1  The  "booster"  consists  of  a  generator  driven  by  a  motor  mechanically  connected  to 
its  armature  shaft.  The  terminals  of  the  generator  are  connected  in  series  with  one  "leg" 
of  the  feed  system.  The  current  in  the  feed  wire  excites  the  field  in  proportion  to  the  amount 
of  current  flowing.  Inasmuch  as  the  armature  is  independently  rotated  in  the  field; 
will  produce  an  e.m.f.,  in  proportion  to  the  excitation,  and  this  e.m.f.,  is  added  to  that 
of  the  feed  system. 


POWER-BOARD  WIRING 


65 


POWER-BOARD  WIRING 

Figure  46  shows  the  power-board  wiring  of  an  installation  comprising  two 
motor-dynamos  with  alternating-current  primaries.  The  primary  circuits  from 
transformers  through  the  double-pole  single-throw  switches  to  motors,  and  the 
secondary,  or  dynamo  circuits  through  field-regulating  rheostats  and  double- 
pole,  double-throw  switches  to  service  mains  are  readily  traceable. 

Figure  47  shows  the  wiring  of  a  power-board,  embracing  two  panel-boards, 
switches,  fuses  and  resistance  units  of  a  "rectifier"  installation.  The  double- 
pole,  single-throw  switch  shown  in  the  upper  right-hand  corner  serves  to  connect 
the  alternating-current  supply  circuit  with  the  electrolytic  rectifier  cells.  The 


Direct  Current 


Rectifier 


/ 

\ 

Rectifier 


FIG.  47. — Power-board  wiring  of  an  electrolytic  rectifier  installation. 

secondary,  or  direct  current  derived  has  the  negative  side  grounded  from  the 
double-pole,  double- throw  switch  shown  in  the  center  of  the  diagram,  while  the 
positive  lead  is  connected  through  resistance  coils  and  fuses  to  the  desired  ser- 
vice assignment. 

Figure  48  shows  a  diagram  of  the  wiring  of  a  power-board  installation  which 
provides  all  necessary  switching  arrangements  for  a  motor-generator  plant 
consisting  of: 

8  motor  generators  with  no- volt  primaries. 

3  of  them  having  385-volt  secondaries. 

3  2oo-volt  secondaries. 

i  5<D-volt  secondary. 

i  1 50- volt  alternating-current  secondary  (for  phantoplex  service). 
The  diagram  shows  the  switch  terminal  connections,  busbar  and  ground  con- 

5 


66 


AMERICAN  TELEGRAPH  PRACTICE 


POWER-BOARD  WIRING 


67 


nections  necessary  to  control  the  various  motor  circuits,  also  the  potential 
leads  from  the  dynamo  ends  of  the  various  units,  which  latter  are  carried  to 
the  desired  service  assignment  in  the  operating-room  via  the  resistance  coil 
racks. 

In  this  particular  installation  the  current  employed  to  operate  single  lines 
and  local  circuits  is  derived  from  the  regular  commercial  no-volt  service,  thus 
obviating  the  employment  of  motor-generators  to  supply  current  for  such 
purposes. 

Where  no- volt  current  is  used  for  the  operation  of  " local"  circuits,  2,000- 
ohm  resistance  coils  are  inserted  in  series  with  the  mains,  and  the  local  instru- 


ftftftftftft 

H  n  n  n  u  u 


ftftftftft 


Voltmeter 


ftftftftftft 

18   II   I!   II   II   II 

a      a      a      a      a      a 

Intermediate  Battery 

ft  ft  Art  ft  ft 

i!  i!  ii  o  n 

en       en       en      era       a 


a=o~ 
0=0 


:  j....-(jsB  £j      j  i.-<S55 

j—  UP 


r*-- "L3h        r-i-f^-i-^ 

,...,  ..,...r.t..r.r-T        •TT--J     lr-r-.J 


FIG.  49. — Auxiliary  power-board,  knife-switch  and  fuse  arrangement. 

ments;  such  as  sounders,  transmitters,  pole-changers,  repeaters,   call-circuit 
relays,  etc.,  are  wound  to  a  resistance  of  150  ohms  each. 

The  potential  mains  leading  from  the  power-board  to  the  operating-room 
are  carried  in  iron  pipe  i  1/2  in.  in  diameter,  the  conductors  for  the  high 
voltage  consist  of  No.  6  B.  &  S.,  copper,  rubber  insulated  and  lead  covered. 
For  the  lower  voltages  the  conductors  consist  of_No.  12  B.  &  S.  copper,  rubber 
insulated  twin-conductor,  lead  covered. 


68 


AMERICAN  TELEGRAPH  PRACTICE 


Where  a  twin-conductor  cable  is  used  to  carry  dynamo  currents  from  the 
power-board  to  the  operating-room,  it  is  customary  so  to  divide  the  circuits 
that  two  "plus"  leads  or  two  "minus"  leads  are  carried  in  one  cable.  This 
method  of  current  distribution  subjects  the  insulation  of  the  conductors  to 
considerably  less  disruptive  strain  than  when  opposing  polarities  are  carried 
in  the  same  cable.  In  some  of  the  larger  telegraph  offices,  the  motor-generator 
equipment  is  located  in  the  basement  of  the  building,  or  in  a  location  remote 
from  the  operating-room.  Control  of  the  machinery  by  the  dynamo  attendant 
necessitates  that  the  power-board  be  located  close  to  the  machines.  A  very 
convenient  provision,  and  one  which  at  the  present  time,  is  considered  good 


3-PhaseA.C. 
WOv60Cycle.     LA. 

F- 


1IOV 


W-  |  -  1 
MeteA  __  < 


BB 


Bus  Bars 

or?  Power  Board,  from 

which  Motor  Ends  of 

Motor-Dynamos  are 

wired. 


FIG.  50. — Typical  power-board  installation. 

practice,  is  to  have  in  the  operating-room,  or  in  a  smaller  room  on  the  same 
floor  in  close  proximity  thereto,  an  auxiliary  power-board  to  which  are 
connected  all  potential  mains  from  the  power-board  proper.  This  arrangement 
gives  the  operating-room  attendants  direct  control  over  current  distribution, 
and  is  of  considerable  utility  in  the  matter  of  making  alterations  in  battery 
assignments. 

The  equipment  of  such  an  auxiliary-board  is  depicted  in  Fig.  49.  At  the 
top  in  the  center  is  shown  a  voltmeter,  and  underneath  it,  a  meter-switch 
common  to  all  potential  leads.  By  moving  the  indicator  of  the  switch  oppo- 
site the  marker  of  the  voltage  and  polarity  intended  to  be  measured,  the  volt- 
meter circuit  is  completed  from  the  desired  potential  conductor  to  ground. 


POWER-BOARD  WIRING  69 

The  double-pole  single-throw,  and  the  single-pole  single-throw  switches  have 
" marker"  cards  mounted  near  them  which  indicate  the  voltage  and  polarity 
of  each  terminal.  In  the  case  of  mains  having  one  polarity  only  (controlled 
by  the  S.  P.  S.  T.  switches)  it  may  be  noted  that  the  circuit  extends  from  the 
full-load  fuse  at  the  bottom  of  the  switch  to  a  small  "bus"  to  which  eight 
service  conductors  are  connected  through  individual  fuses. 

Figure  50  shows  the  external  connections  of  a  typical  installation  where 
both  1 10- volt  direct-current  and  200- volt  alternating-current  commercial 
voltages  are  available  for  the  purpose  of  operating  motor-generators.  On 
the  left,  the  200- volt  alternating-current  supply  wires  are  shown  connected 
through  line  fuses,  three-pole  single-throw  switch,  wattmeter,  and  auto- 
starter  to  the  motor  terminals.  A  direct-current  generator  with  an  output  of 
no  volts,  directly  connected  to  and  driven  by  the  alternating-current  motor 
has  its  voltage  impressed  on  the  busbars  B-B  when  the  switch  6*3  is  thrown  to 
the  right.  The  external  connections  of  the  generator  field  rheostat,  current 
regulator,  and  under-load  automatic  circuit-breaker  are  shown  in  proper 
order.  (The  internal  connections  of  these  various  current-controlling 
devices  are  described  in  detail  in  Chapter  III.)  The  eight  or  more  motor- 
generators  or  dynamotors  usually  required  to  operate  the  different  telegraph 
circuits  derive  their  motor  operating  current  from  the  busbars  B-B.  The 
connections^made  between  busbars  and  motor  ends  of  motor-generators  may 
be  traced  by  aid  of  diagrams  25,  26  and  27. 

In  the  installation  illustrated  in  Fig.  50,  the  motor-generators  connected 
to  the  busbars  may  be  operated  either  from  the  no- volt  current  generated  on 
the  ground  as  above  described,  or  may  be  operated  from  the  no- volt  "  street " 
mains.  In  the  latter  case  the  switch  S2  is  closed,  and  the  switch  6*3  is  thrown 
to  the  left. 


CHAPTER  VI 

CIRCUITS   AND    CONDUCTORS;   THE   ELECTRIC    CIRCUIT;   THE 
MAGNETIC  CIRCUIT;  ELECTROMAGNETS 

The  general  statement  of  Ohm's  law  given  under  the  heading  of  "  Units 
and  Symbols"  in  Chapter  I  provides  a  means  whereby  the  properties  or 
characteristics  of  electric  circuits  may  be  investigated. 

An  electric  circuit  such  as  that  illustrated  in  Fig.  51,  possesses  capacity, 
resistance,  and  inductance.  Also  as  the  circuit  has  an  e.m.f.  applied  to  it, 
there  is  potential  and  current  to  reckon  with.  In  the  order  given  the  symbols 
representing  these  various  factors  are: 

Capacity,      "C"  (farads) 
Resistance,   "R"  (ohms) 
Inductance,   (h)    (henries) 
E.M.F.,          (£)   (volts) 
Current,         (/)    (amperes) 

In  what  follows,  where  diagrams  accompany  descriptions  of  different  cir- 
cuit arrangements,  sources  of  e.m.f.  will  be  represented  as  in  Fig.  51.  It  is  to 
be  understood,  however,  that  so  long  as  we  are  dealing  with  direct  currents, 
the  method  employed  to  produce  the  difference  of  potential  is  immaterial,  and 
the  circuit  depicted  in  Fig.  51  might  be  shown  as  in  Fig.  52,  where  a  direct- 
current  dynamo  is  the  source  of  e.m.f. 

An  electric  circuit,  so  called,  consists  of  a  path  composed  of  a  conducting 
wire,  or  of  several  wires  connected  together,  through  which  an  electric  current 
is  said  to  flow  from  a  given  point;  along  the  conducting  path  and  back  to  the 
starting-point  (Fig.  53). 

A  circuit  which  may  be  " opened"  or  " closed"  at  will  has  connected  in  its 
conducting  path  a  "key"  or  "switch"  as  illustrated  in  Fig.  54. 

A  circuit  is  said  to  be  "open"  when  its  conducting  path  is  broken,  or 
otherwise  disconnected,  and  "closed"  when  the  conducting  path  is  complete, 
permitting  electrical  action  to  take  place. 

A  "grounded"  circuit  is  one  such  as  that  illustrated  in  Fig.  55,  where  both 
terminals  of  the  source  of  e.m.f.  are  grounded. 

When  a  circuit  is  divided  into  two  or  more  parts,  it  is  called  a  "divided" 
circuit,  and  each  part  will  carry  a  portion  of  the  current,  see  Fig.  56. 

Voltage,  resistance,  and  current  values  in  electric  circuits  may  be  deter- 

70 


CIRCUITS  AND  CONDUCTORS 


71 


mined  by  means  of  Ohm's  law,  by  employing  the  formulae  evolved  from  the 
statement  of  principles  before  referred  to.     In  their  shortest  form  these  are: 


E=IXR. 


c  z      c  z      c  z      cz 


FIGS.  51-59. 

Unit  sources  of  e.m.f .  may  be  arranged  in  different  ways  in  order  to  obtain 
desired  results.  The  various  arrangements  outlined  in  the  diagrams  which 
follow,  apply  equally  to  dynamos,  chemical  batteries,  and  to  other  sources  of 
continuous  currents. 

Where  chemical  batteries  are  employed  for  practical  purposes,  their  com- 
paratively high  internal  resistance  per  cell;  in  certain  applications  makes  it 
desirable  to  so  arrange  the  elements  of  a  battery  that  the  internal  resistance 


72  AMERICAN  TELEGRAPH  PRACTICE 

of  the  battery  as  a  whole  is  less  than  the  sum  of  the  individual  resistances  of 
all  of  the  cells  comprising  the  battery. 

In  Fig.  57  the  positive  and  negative  elements  of  each  cell  are  connected  in 
"series."  It  is  apparent  that  the  circuit  is  made  up  of  the  conducting  wire, 
positive  and  negative  elements  of  each  cell,  and  the  electrolyte  intervening 
between  the  elements  of  each  cell.  Therefore,  the  current  produced  by  an 
individual  cell  in  traversing  the  circuit  is  required  to  pass  through  one  after 
the  other  of  the  cells  of  the  battery. 

If  we  consider  that  the  battery  shown  in  Fig.  57  consists  of  gravity  cells, 
each  having  an  e.m.f.  of  1.07  volts  and  an  internal  resistance  of  2.5  ohms, 
and  that  the  "  external"  circuit  or  conducting  wire  has  a  resistance  of  10  ohms 
it  is  possible  by  means  of  the  formula 


to  calculate  the  value  of  the  current  in  amperes,  flowing  in  the  circuit;  thus: 

£  =  1.07X4  =  4.28  volts. 
R  =  10+  (2.5X4)  =  20  ohms. 
and 

4.28 

-  =  0.214  ampere,  or  214  milliamperes. 

The  e.m.f.  of  a  cell  is  independent  of  the  size  of  the  elements  consti- 
tuting the  cell  (the  copper  and  the  zinc  electrodes).  This  means  that  a  cell 
the  size  of  a  tea  cup  has  the  same  e.m.f.  as  a  cell  of  the  regulation  size  or  larger. 
The  internal  resistance,  however,  differs  considerably.  Also,  the  life  of  the 
cell  and  the  current  that  may  be  derived  in  each  case  makes  the  larger  size  of 
greater  .utility. 

In  the  arrangement  shown  in  Fig.  57,  the  cells  are  connected  so  that  the 
greatest  quantity  of  current  is  obtainable  where  the  external  circuit  has  a 
comparatively  high  resistance. 

In  the  arrangement  shown  in  Fig.  58  the  cells  are  connected  in  "  multiple," 
that  is,  all  of  the  positive  electrodes  are  connected  together  and  all  of  the 
negative  electrodes  are  likewise  joined,  thus  in  effect  making  one  large  cell 
in  which  all  of  the  zincs  constitute  one  element  and  all  of  the  coppers  the  other 
element.  This  arrangement  produces  the  largest  quantity  of  current  through 
an  external  circuit  of  comparatively  low  resistance.  Assuming  that  each  cell 
has  an  e.m.f.  of  1.07  volts,  the  total  e.m.f.  of  the  four  cells  arranged  in  series 
(Fig.  57)  will  be  4.28  volts,  while  the  voltage  derived  from  the  multiple  arrange- 
ment (Fig.  58)  will  be,  simply  the  voltage  of  one  cell,  or  1.07  volts.  In  each 
case,  however,  the  total  internal  resistance  will  differ,  as  in  the  series  arrange- 
ment the  resistance  of  each  cell  (2.5  ohms)  is  added  to  that  of  the  others, 
making  a  total  resistance  of  10  ohms,  while  the  total  internal  resistance  of 


CIRCUITS  AND  CONDUCTORS  73 

the  four  cells  arranged  in  multiple,  due  to  quadrupling  the  size  of  the  plates,  or 
elements,  would  be  but  a  fraction  of  an  ohm,  as  will  be  explained  in  connection 
with  calculations  pertaining  to  the  resistance  of  joint  circuits. 

Figure  59  shows  a  multiple-series  arrangement  of  cells  in  which  two  groups 
of  two  cells  each  in  series  are  connected  to  the  external  circuit  in  multiple. 
In  this  case  the  derived  e.m.f.  would  be  1.07  +  1.07  =  2.14  volts,  and  the  total 
resistance  of  the  battery  2  i/:  ohms. 

The  total  voltage  of  a  battery  is  dependent  upon  the  number  of  cells  in 
"series."  If  it  is  desired  to  obtain  a  greater  current  in  afhperes  from  a  bat- 
tery, without  changing  the  e.m.f.  (voltage)  additional  cells  must  be  placed  in 
parallel  or  multiple,  as  shown  in  Fig.  58.  Consider  for  instance,  that  a  given 
battery  arranged  as  shown  in  Fig.  57  has  100  cells  instead  of  four  as  there 
illustrated.  At  the  terminals  of  the  battery  there  will  be  a  total  e.m.f.  of 

1.07X100  =  107  volts. 

If,  then  it  is  desired  to  increase  the  "current"  without  increasing  the  "volt- 
age" an  additional  series  of  cells  may  be  connected  in  parallel  to  the  first 
series,  thus  adding  its  current  to  the  circuit  without  increasing  the  e.m.f.  of 
the  battery  as  a  whole.  Additional  rows  of  cells  in  series  may  be  added  as 
indicated  in  Fig.  58,  where  four  rows  of  one  cell  in  series  are  connected  in 
parallel.  This  battery  would  be  referred  to  as  having  one  cell  in  series  and 
four  cells  in  parallel. 

By  means  of  simple  formulae,  the  current  obtainable  from  a  battery  con- 
nected in  a  given  manner  may  be  calculated  with  sufficient  accuracy  for  all 
practical  purposes. 

Let  E  =  e.m.f.  of  one  cell, 

r  =  Internal  resistance  of  one  cell, 
R  ='External  resistance  of  the  circuit,  if  any. 

Then  for  n  cells  connected  in  series,  the  current  in  the  circuit  will  be  repre- 
sented by  the  formula: 


nr+R 

With  one  cell  on  short  circuit  and  no  appreciable  external  resistance,  the  cur- 
rent is: 


In  the  case  of  long  telegraph  circuits  where  nr  is  small  as  compared  with  R, 
the  current  obviously  increases  in  proportion  to  the  number  of  cells  employed, 
and: 

nE 


74  AMERICAN  TELEGRAPH  PRACTICE 

The  value  of  r  is  approximately  inversely  proportional  to  the  area  of  the  plates 
separated  by  the  electrolyte  and  directly  proportional  to  their  distance  apart, 
therefore,  if  the  total  area  of  the  positive  and  the  negative  electrodes  is  in- 
creased by  connecting  cells  in  parallel,  the  general  application  of  the 
formula  is: 

E  aE 


> 


where  the  area  of  the  plates  of  one  cell  is  increased  a  times. 
Now,  if  N  =  the  total  number  of  cells  in  the  battery, 

n  =  the  number  of  cells  in  series, 
P  =  the  number  of  rows  in  parallel, 

then  the  internal  resistance  of  the  battery 

nr 
^~P 

To  so  arrange  cells  that  the  maximum  current  may  be  obtained  in  a  given 
external  circuit,  make 

-p  equal  to  the  resistance  of  the  external  circuit 
In  any  given  circuit 


total  e.m.f. 

— -= r-r         and  for  any  given  arrangement 

total  resistance,  J  l 


of  cells 


T_nE        _ 
~  nr         nr+PR 


. 

To  determine  the  maximum  current  in  amperes  obtainable  from  a  given 
battery  having  N  cells,  through  an  external  circuit  of  resistance  R 


E  IN 
7VI5 


Rr 

• 
In  practice  the  cells  of  a  battery  may  be  connected  in  three  different 

ways,  (i)  all  cells  in  series,  (2)  all  cells  in  parallel,  (3)  some  cells  in  parallel, 
and  some  in  series. 

If  n  represents  the  number  of  cells  in  series  and  P  the  number  of 
cells  in  parallel;  obviously  the  total  number  of  cells  in  the  battery  equals  the 
product  of  n  and  P,  or  nXP. 


CIRCUITS  AND  CONDUCTORS  75 

The  c.m.f.  of  a  battery  equals  the  e.m.f.  of  one  cell  multiplied  by  the 
number  of  cells  in  series. 

The  resistance  in  ohms,  of  a  battery  equals  the  number  of  cells  in  series 
multiplied  by  the  resistance  of  one  cell,  divided  by  the  number  of  cells  in 
multiple,  or  parallel.  For  example,  a  battery  of  48  cells,  each  having  an 
e.m.f.,  of  1.07  volts  and  an  internal  resistance  of  2  1/2  ohms,  connected  in 
series,  has  a  total  resistance 

r  =  2. 5X48=120  ohms. 
And  an  e.m.f. 

£=1.07X48  =  51.36  volts. 
The  same  battery  with  all  cells  connected  in  parallel  would  have 

1X21/2     t          . 

r  = =(0.052)  ohms, 

45 

and 

E  =  i  .07  X  i  =  i  .07  volts. 

A  battery  of  50  cells  arranged  in  ten  rows  of  5  in  series  (see  Fig.  59) 
would  have 

r  = -^-=1.25  ohms 

£=5X1.07  =  5.35  volts. 

A  typical  example  of  actual  telegraphic  practice  would  be  to  find  the 
number  of  cells  of  gravity  battery  required  to  furnish  a  current  of  45  milli- 
amperes  (0.045  ampere)  in  a  circuit  having  a  conductor  resistance  of  800 
ohms,  and  a  total  instrument  resistance  of  600  ohms.  Taking  the  e.m.f. 
per  cell  to  be  1.07  volts,  and  the  internal  resistance  per  cell  as  2  1/2  ohms,  we 
have 

N  =  the  number  of  cells  required, 

R  =  the  total  external  resistance, 

r  =  the  internal  resistance  per  cell, 

E  =  the  e.m.f.  per  cell, 

7  =  the  current  required  in  the  circuit.     , 

Then 

AT  -^  1,400 

#  =  -£ =  -  "  =  65  cells 

E  1.07  / 

T— r          —  —  2  1/2 
1  0.045 

Where  the  resulting  figures  contain  a  fraction,  the  nearest  whole  number  may 


76  AMERICAN  TELEGRAPH  PRACTICE 

be  taken  as  the  practical  requirement.     The  result  obtained  in  the  last  example 
may  be  "proved"  by  means  of  Ohm's  law, 

•p 
7  =    ,  as  in  this  case, 


£  =  65X1.07  =  69.55  volts, 

72  =  800+600+162.5  =  1,562.5  ohms, 


and 


'      =0.44+  ampere,  or  45  milliamperes, 

thus  checking  the  original  calculation  and  proving  that  the  determination  was 
correct. 

The  resistance  of  telegraph  lines  invariably  is  considerably  greater  than  the 
internal  resistance  of  the  battery  employed,  and  as  stated  in  connection  with 
Fig.  57,  the  cells  are  arranged  in  series.  Occasionally,  however,  a  condition 
arises  where  an  external  circuit  having  comparatively  low  resistance  has  to  be 
supplied  with  a  current  somewhat  greater  than  that  required  in  ordinary  tele- 
graph work,  and  where  such  requirements  have  to  be  met  by  suitable  primary 
battery  arrangements,  the  parallel  or  series-parallel  coupling  of  cells  may  be 
used  to  advantage. 

Conductor  Resistance. — The  resistance  of  a  conducting  wire  is  proportional 
to  its  length.  If  the  resistance  of  a  mile  of  copper  telegraph  wire  is  10  ohms, 
that  of  100  miles  of  the  same  wire  will  be  10X100  =  1,000  ohms. 

The  resistance  of  any  given  conductor  is  inversely  proportional  to  the  area 
of  its  cross-section,  and  in  the  case  of  round  wires,  is  inversely  proportional  to 
the  square  of  the  diameter  of  the  conductor.  A  No.  9  copper  wire  (B.  &  S. 
gage)  having  a  diameter  of  0.114  m-  nas  a  resistance  of  4.39  ohms  per  mile  at 
a  temperature  of  75°  F.  A  wire  having  twice  that  diameter  or  0.228  in.  would 
have  a  resistance  but  one-fourth  that  of  the  former. 

The  resistance  with  which  a  conducting  wire  of  given  length  and  given 
cross-sectional  area  opposes  the  passage  of  a  current  of  electricity,  depends 
upon  the  material  of  which  the  conducting  wire  is  made  or,  in  other  words, 
depends  upon  the  specific  resistance  of  the  material. 
Let  R  represent  the  resistance  of  the  conductor  in  ohms, 

p  represent  specific  resistance  of  the  conductor, 
A  represent  cross-section  of  the  conductor, 
/   represent  length  of  the  conductor. 

Then  R  =  f)A 

or  P=Rj 


CIRCUITS  AND  CONDUCTORS  77 

If  the  length  (/)  is  measured  in  inches,  and  the  cross-section  (A)  in  square 
inches,  then  p  is  the  resistance  of  an  inch  cube  of  the  conductor. 

In  telegraph  practice  it  is  customary  to  refer  to  specific  resistance  in 
terms  of  the  mile-ohm,  which  signifies  the  weight  in  pounds  of  a  conductor 
having  a  length  of  i  mile  and  a  resistance  of  i  ohm. 

In  those  instances  where  specific  resistance  is  referred  to  in  terms  of  ohms 
per  mil-foot  (the  resistance  of  a  round  wire  i  ft.  long  and  o.ooi  in.  in  diameter) 
length  (7)  is  measured  in  feet,  and  area  (/I)  in  circular  mils.     If  the  length  (7) 
of  a  conductor  is  measured  in  centimeters  and  the  area  (^4)  in  square  centimeters 
p  is  the  resistance  of  a  centimeter  cube  of  that  conductor. 

The  term  conductance  is  used  as  the  inverse  of  resistance.  A  conducting 
wire  whose  resistance  is  R  ohms  is  said  to  have  a  conductance  of 


^ 
K 

Specific  conductivity  is  the  reciprocal  of  specific  resistance,  and  if  X  repre 
sents  specific  conductivity, 


CONVERSION  FACTORS 

i  mil  =  0.02  54  mm.  =0.001  in. 
i  mm.  =39.37  mils  =  o.o3937  in. 
i  cm.  =0.3937  in.  =0.328  ft. 
i  in.  =  25.4  mm.  =0.083  ft.  =  2.  54  cm. 
i  circular  mil  =  0.7854  sq.  mil  =  0.0005067  sq.  mm. 
i  sq.  mil  =  1.2  73  cir.  mils  =  0.000645  scl-  ram.  =0.000001  sq.  in. 
i  sq.  mm.  =  1,973  cir-  mils  =  I>55o  sq-  mil  =  0.00155  sq.  in. 
i  sq.  cm.  =  197,300  cir.  mils  =  0.155  scl-  in.  =0.00108  sq.  ft. 
i  sq.  in.  =  1,273,  240  cu~-  nrils=  6.451  sq.  cm.  =0.0069  sq.  ft. 
i  cir.  mil-foot  =  0.0000094248  cu.  in. 
i  cu.  cm.  =  o.o6i  cu.  in. 
i  cu.  in.  =  16.39  cu-  cm- 
The  microhm  =  0.0000001  ohm. 

Microhms  per  inch  cube  =  0.393  7  X  microhms  per  centimeter  cube. 
Pounds  per  mile-ohm  =  5  7.  07  X  microhms  per  cm.  cu.  X  specific  gravity. 
Ohms  per  mil-foot  =  6.01  5  X  microhms  per  cm.  cu. 

The  square  of  the  diameter  of  a  given  wire  expressed  in  mils  (o.ooi  in.) 
gives  the  circular  mils. 


78  AMERICAN  TELEGRAPH  PRACTICE 

Problems  involving  comparisons  of  conductors  having  unequal  resistances, 
require  that: 

The  square  of  the  diameter  of  each  wire  be  multiplied  by  the  length  of  the 
other.  The  ratio  of  the  resistance  of  one  wire  to  that  of  the  other  is  obtained  by 
dividing  the  products  thus  obtained.  The  resistance  value  sought  is  determined 
by  multiplying  the  ratio  by  the  known  resistance. 

For  example: 

A  given  wire  of  50  mils  diameter  and  20  miles  long  has  a  resistance  of  200  ohms.  An- 
other wire  has  a  diameter  of  40  mils  and  is  40  miles  long.  Assuming  that  the  wires  are 
made  of  the  same  material  what  is  the  resistance  of  the  second  wire? 

Solution: 

*        5  o2X  40=  100,000,  relative  resistance  of  first  wire. 
=  32,ooo,  relative  resistance  of  second  wire. 


100.000 

---  =  3.  125,  ratio  of  second  wire  to  the  first. 

and 

200X3.125  =  625  ohms. 

As  an  example  of  calculating  the  required  diameter  in  mils  of  a  conducting 
wire_,  assume  that  a  wire  i  mile  (5,280  ft.)  long  has  a  diameter  of  100  mils  and 
a  resistance  of  10  ohms;  what  would  be  the  diameter  of  a  wire  made  of  the  same 
material  of  which  a  length  of  i  mile  has  a  resistance  of  40  ohms? 

Solution: 

—  =  4  (ratio  of  resistances) 

5,280 

-  =  1,320  ft. 


and 

— 


2,500,   which   is   the   square   of   the  diameter  of  the 


second  wire, 
and 


\/2,5oo  =  5o  (mils) 


CIRCUITS  AND  CONDUCTORS 


79 


SPECIFIC  RESISTANCE,  RELATIVE  RESISTANCE,  AND  RELATIVE  CONDUCTIVITY  OF 

CONDUCTORS 
Pertaining  to  Mathiessen's  standard 


Resistance  i 

n  microhms 

at  o 

0    /~* 

Relative 

Relative 

l\/Tof  olo 

'  t 

j     ,  •   •, 

IVietaiS 

resistance, 

conductivity, 

Centimeter 

Inch  cube 

per  cent. 

per  cent. 

cube 

Silver,  annealed  

i-47 

o-579 

92-5 

108.2 

Copper  annealed 

i   ^ 

o.  610 

97  •  5 

IO2.6 

Copper  (Matthiessen's  standard). 

•  00 

1-594 

0.6276 

y  /    o 
IOO 

IOO.O 

Gold  (99  .  9  per  cent,  pure)  

2.  2O 

0.865 

138 

72.5 

Aluminum  (99  per  cent.  pure)..  . 

2.56 

i  .01 

161 

62.1 

Zinc  

5-75 

2.26 

362 

27.6 

Platinum,  annealed  

8.98 

3-53 

565 

17.7 

Iron     

o  .  07 

•3..  C7 

57° 

17.6 

Nickel  

v      / 

12.3 

O     O  / 

4-85 

778 

12.9 

tin     

I3  •  I 

5.16 

828 

12.  I 

Lead  

20.4 

8.04 

1,280 

7.82 

Antimony 

3^2 

13   O 

2,210 

4-53 

Mercury  

O  0  • 

94.3 

O    V 

37-1 

5,930 

1.69 

Bismuth 

130  o 

<?I    2 

8,220 

I  .  22 

Carbon   (arc  light) 

AO       .  w 

4  ooo  .  o 

o     * 

i  ^oo  (aDDr  ) 

JOV      \UlrJJLJ     / 

At  1 8°  C.  pure  water  has  a  resistance  of  2,650  ohms  per  cm.cu.,  and  1,050 
ohms  per  inch  cube.  The  following  example  will  illustrate  the  value  of  the 
above  table  in  connection  with  the  formula  given  on  page  77.  According 
to  the  table  the  specific  resistance  of  iron  is  3.57  microhms  per  cubic  inch, 
this  is  equal  to  0.00000357  ohms.  Required  the  resistance  of  a  wire  100  ft. 
long  and  o.oio  in.  in  diameter.  By  employing  the  forfnula 


we  have 


and 


p =0.000003  5  7 

nd2  3.i4i6X.oio2 

A=  —  =  —       —  =  0.00007854  sq.  in. 
4       4 


I   =  100  ft.  =  1,200  in. 

0.00000357X12 
R  =  —     —^  --  = 

0.00007854 


ohm. 


The  commercial  standard  of  conductivity   (Mattheissen's)   is  a  copper 
wire  having  the  following  properties  at  a  temperature  of  o°  C. 


80 


AMERICAN  TELEGRAPH  PRACTICE 


Relative   conductivity 100  per  cent. 

Length : i  meter. 

Weight i  grm. 

Specific  gravity 8.89. 

Resistance 0.141729  ohms. 

Specific  resistance 1-594  microhms  per  cm.  cu. 

Resistance  Affected  by  Heating. — Changes  of  temperature  affect  the  con- 
ducting properties  of  metals.  Most  of  the  pure  metals  increase  in  resistance 
approximately  0.4  per  cent,  for  a  rise  in  temperature  of  i°  C.  German  silver 
wire  which  is  used  in  making  resistance  coils  for  telegraph  purposes  has  a 
temperature  coefficient  of  only  about  i/io  that  of  pure  metals,  or  0.00044 
for  i°  C. 


TEMPERATURE  COEFFICIENTS 

Let    RI  represent  the  resistance  at  O°, 
Rz  represent  the  resistance  at  t°, 
a  represent  the  temperature  coefficient  of  the  material, 

then    R2=Ri  (i+af). 

100  a  is  the  percentage  of  change  in  resistance  per  degree  change  in  tempera- 
ture. Where  the  resistance  of  the  material  at  the  higher  temperature  is 
known,  the  resistance  of  the  same  material  at  a  lower  temperature  may  be 
determined  by  means  of  the  formula: 

Rz 


The  following  values  of  the  temperature  coefficients  of  various  metals  have 
been  determined  in  degrees  Centigrade  and  Fahrenheit. 


Pure  metals 

Centigrade  a 

Fahrenheit  a 

Silver,  annealed  

o  00400 

O    OO222 

Copper,  annealed 

o  004  2  8 

o  00242 

Gold  (99  .  9  per  cent.)  
Aluminum,  (99  per  cent.)  
Zinc     

0.00377 
0.00423 
o  00406 

O.OO2IO 
0.00235 

o  00226 

Platinum  annealed 

o  0024.7 

o  00137 

Iron 

o  006  2  5 

O    OO347 

Nickel  
Tin          

0.00620 
o  00440 

0.00345 
O.OO245 

Lead 

o  004  i  i 

o  00228 

Antimony 

o  00380 

o  00216 

Mercury  

0.00072 

o  .  00044 

Bismuth  

O    OO3  ^4 

0.00197 

CIRCUITS  AND  CONDUCTORS 


81 


It  is  important  when  calculating  the  resistance  of  a  given  material,  noted  at 
different  temperatures,  to  use  the  temperature  coefficient  based  on  the  "  scale  " 
(Fahrenheit  or  Centigrade)  which  was  employed  in  recording  the  difference  in 
temperature. 
Example : 

The  resistance  of  a  length  of  copper  wire  at  72°  F.  is  no  ohms.  What 
would  be  its  resistance  at  a  temperature  of  100°  F.? 

Solution: 

J?i  =  IIO, 

^  =  100  —  72  =  28, 
a  =  o.  00242, 

and,  substituting,  we  have: 

-R2  =  no  (1+0.00242X28) 
=  110X1 .06770, 
=  117  ohms  (approx.). 

The  following  table  gives  the  resistance  of  sizes  oooo  to  40,  American, 
or  Brown  and  Sharpe  (B.  &  S.)  gage,  of  pure  copper  wire  at  a  specific  gravity 
(sp.  gr.)  of  8.9,  and  at  a  temperature  of  75°  F.  (23.8°  C.).  Sixty  degrees 
Fahrenheit,  or  15.5°  C.  is  the  standard  temperature  for  measuring  the 
electrical  resistance  of  wire  for  general  telegraphic  purposes,  as  that  value  is 
assumed  to  be  the  average  temperature  of  air. 

DIMENSIONS  AND  RESISTANCE  OF  PURE  COPPER  WIRE 
(Specific  gravity  8.9;  resistance  at  75°  F.) 


American  or 
B.  &  S.  gage 

Diameter  d 
in  mils,  i  mil 

Circular 
mils  (d2) 

Pounds  per 

1,000  ft. 

Feet  per 
pound 

R  ohms  per 

1,000  ft. 

=  .  ooi  in. 

oooo 

460.0 

211,600 

639- 

1-56 

•05 

ooo 

409.6 

167,805 

507- 

i-97 

.06 

oo 

364.8 

133,079 

402. 

2.49 

.08 

0 

324-9 

*05,592 

3J9- 

3-13 

.  10 

I 

289.3 

83,694 

253- 

3-95 

.12 

2 

257.6 

66,373 

200. 

5-o 

.16  ' 

3 

229.4 

52,634 

159- 

6-3 

.  2O 

4 

204.3 

41,742 

126. 

7-9 

•25 

5 

181.9 

33,102 

100. 

IO.O 

•31 

6 

162.0 

26,250 

79- 

12.6 

.40 

7 

144-3 

20,816 

63. 

15-9 

•50 

8 

128.5 

16,509 

50. 

20. 

.63 

9 

114.4 

J3>094 

40. 

25. 

•79 

10 

101  .9 

10,381 

31- 

32. 

i. 

ii 

90.7 

8,234 

25- 

40. 

i  .  26 

12 

80.8 

6,530 

20. 

50. 

i-59 

13 

72.0 

5,i78 

15-6 

64. 

2.0O 

14 

64.  i 

4,107 

12.4 

81. 

2-53 

82 


AMERICAN  TELEGRAPH  PRACTICE 


DIMENSIONS  AND  RESISTANCE  OF  PURE  COPPER  WIRE — (Continued) 
(Specific  gravity  8.9;  resistance  at  75°  F.) 


American  or 
B.  &  S.  gage 

Diameter  d 
in  mils,  i  mil 
=  .  ooi  in. 

Circular 
mils    d2) 

Pounds  per 
1,000  ft. 

Feet  per 
pound 

R  ohms  per 

1,000  ft. 

15 

57-1 

3,257 

9.8 

IO2. 

3-2 

16 

50.8 

2,583 

7-8 

128. 

4-0 

17 

45-3 

2,048 

6.2 

161. 

5- 

18 

40.3 

1,624 

4-9 

204. 

6-4 

19 

35-4 

1,252 

3.78 

264. 

8.0 

20 

32.0 

I,O2I 

'      3-09 

324- 

10.  2 

21 

28.5 

810 

2-45 

408. 

12.8 

22 

25-3 

643 

1.94 

SIS- 

16.2 

23 

22.6 

509 

1-54 

650. 

2O.4 

24 

20.  1 

404 

I.  22 

819. 

25-7 

25 

17.9 

320 

•97 

1,033. 

32-4 

26 

15-9 

254 

•77 

1,302. 

40.8 

27 

14.2 

2OI 

.61 

1,642. 

51-5 

28 

12.6 

1  6O 

.48 

2,071. 

64- 

29 

n-3 

127 

.38 

2,611. 

82. 

30 

IO.O 

IOO 

•30 

3,294. 

I03. 

31 

8.9 

80 

.24 

4,152. 

I29. 

32 

7-9 

63 

.19 

5,237. 

I64. 

33 

7-i 

50 

•15 

6,603. 

207. 

34 

6-3 

40 

.  12 

8,328. 

26l. 

35 

5-6 

32 

.  IO 

10,500. 

329. 

36 

5-o 

25 

.08 

13,240. 

415. 

37 

4-5 

20 

.06 

16,691  . 

524. 

38 

4.0 

16 

•OS 

20,850. 

660. 

39 

3-5 

12 

.04 

26,300. 

832. 

40 

3-i 

10 

•03 

33,200. 

1,050. 

From  the  foregoing  it  is  evident  that  conductor  resistance  depends  upon 
dimension,  composition,  and  temperature  of  the  conductor. 

So  far  as  external  conductors  in  aerial  lines  and  cables  are  concerned  the 
average  difference  in  temperature  between  summer  and  winter  months,  say 
100°  F.  and  22°  F.,  results  in  an  increase  of  resistance  while  the  higher  tempera- 
ture prevails,  of  about  26  per  cent,  for  iron  wire,  and  18  per  cent,  for  copper 
wire. 

Where  the  windings  of  resistance  coils  and  of  electromagnets  are  involved 
the  temperature  of  the  conducting  wire,  or  rather  the  variation  in  the  tempera- 
ture of  the  wire  is  always  a  factor  to  be  reckoned  with.  The  use  to  which 
resistance  coils  are  put  is  such  that  frequently  the  temperature  of  individual 
coils  may  rise  above  150°  F.  or  65°  above  normal  (75°  F.  or  23.8°  C.). 

Joint-resistance. — Referring  to  Fig.  60,  where  a  source  of  e.m.f.  has  both 
of  its  terminals  joined  by  two  conducting  wires.  If  the  several  conducting 


CIRCUITS  AND  CONDUCTORS  83 

wires  are  of  equal  length  and  cross-section,  composed  of  the  same  material 
and  at  equal  temperatures,  the  current  will  divide  equally  between  the  two, 
and  the  electrical  resistance  of  the  joint-path  will  be  the  same  as  if  there  were 
but  one  conductor  of  the  same  length  and  of  a  cross-section  equal  to  the  total 
of  the  cross-sections  of  the  two  individual  conductors.  The  current,  therefore, 
existing  in  each  conducting  wire  is  in  the  same  proportion  to  the  total  current 
circulating  as  the  sectional  area  of  one  branch  is  to  the  total  sectional  area  of 
the  joint-path. 

It  is  obvious  that  when  a  circuit  is  divided  into  two  or  more  branches, 
variations  in  the  characteristics  of  the  individual  conductors  of  the  joint 
circuit,  determine  the  amount  of  current  flowing  in  each  branch.  Thus,  one 
of  the  branches  may  be  of  greater  length  than  the  others,  or  the  cross-sectional 
area  of  one  may  be  greater  than  that  of  the  others,  or  there  may  be  involved  a 
difference  of  temperature  sufficient  to  increase  or  decrease  the  resistance  of 
one  of  the  conductors  as  compared  with  the  electrical  resistance  of  another  of 
the  conductors  of  equal  dimension  and  of  the  same  composition. 

A  derived  or  branch  circuit  is  in  effect  a  shunt  circuit,  see  Fig.  61. 

In  a  case  such  as  that  illustrated  in  Fig.  61,  it  is  evident  that  the  current 

R. 


FIG.  60.  FIG.  61.  .     FIG.  62. 

from  the  battery  is  shunted  by  the  wire  A-B,  and,  if  we  assume  that  the  compo- 
sition and  dimensions  of  the  wire  in  the  longer  loop  and  in  the  shorter  circuit 
are  identical,  it  is  obvious  that  a  greater  portion  of  the  total  current  circulating 
will  exist  in  the  shorter  path.  There  are  definite  laws  for  determining  the 
resistance  values  of  shunt  circuits,'  where  it  is  desired  by  this  means  to  regulate 
the  amount  of  current  flowing  in  circuits  in  which  a  shunt  path  forms  a  part 
of  the  joint  circuit.  These  laws  shall  be  considered  presently. 

There  exists  a  popular  fallacy  in  regard  to  the  circulation  of  electric  currents, 
which  in  the  minds  of  those  not  familiar  with  electrical  laws  causes  confusion, 
that  is  "that  a  current  of  electricity  always  takes  the  path  of  least  resistance." 
The  truth  is  that  the  major  portion  of  the  current  flowing  traverses  the  path 
of  least  resistance,  but  the  current  as  a  whole  divides  between  the  various 
paths  in  proportion  to  their  electrical  resistances  individually.  The  relative 
strengths  of  current  flowing  in  two  branches  of  a  circuit  (Fig.  60)  is  inversely 
proportional  to  their  resistances,  and  on  the  other  hand,  proportional  to  their 
conductances. 

If  the  resistance  of  RI  in  Fig.  60  is  20  ohms,  and  RZ,  30  ohms, then  the 
portion  of  the  total  current  flowing  in  RI  will  be  "as  20  is  to  30,"  or,  three- 
fifths  of  the  total  current  will  flow  through  RI  and  two-fifths  through  R2. 


84 


AMERICAN  TELEGRAPH  PRACTICE 


In  Fig.  62  the  joint  resistance  of  the  divided  circuit  between  A  and  B 
will  be  less  than  the  individual  resistance  of  either  branch,  as,  through  this 
portion  of  the  circuit  the  current  has  a  joint  path  equaling  in  sectional  area 
the  sum  of  the  sectional  areas  of  each  conductor  taken  singly.  The  joint- 
conductance  will  be  the  sum  of  the  two  individual  conductances.  The  state- 
ment of  a  law  by  means  of  which  the  joint-resistance  may  be  determined  is : 

The  joint-resistance  of  a  divided  conductor  is  equal  to  the  product  of  the  two 
separate  resistances,  divided  by  their  sum. 

In  general,  this  is  referred  to  as  the  Law  of  shunts. 

In  Fig.  62  if  the  branch  R\  has  a  resistance  of  100  ohms*  and  the  branch  R^, 
a  resistance  of  200  ohms,  then,  where  R  equals  the  value  of  the  joint-resistance 
in  ohms, 

R  = 


100X200 

100+200 
2O,OOO 


300 


66  2/3  ohms. 


As  illustrated  in  Fig.  63,  the  same  result  may  be  ascertained  graphically. 
If  two  perpendiculars  are  erected  at  the  extremities  of  a  base  line  as  shown , 
each  perpendicular  representing  in  height  the  value  of  the  resistance  of  one 


200  Ohms 


Ohms 


FIG.  63. 

of  the  conductors  of  a  divided  circuit  and  two  diagonals  drawn  as  illustrated, 
a  perpendicular  extending  from  the  base  line  to  the  point  of  intersection  of  the 
two  diagonals  will  indicate  the  value  of  the  joint-resistance  of  the  two  branches. 
A  line  drawn  parallel  to  the  base  line  and  extending  between  the  two  outside 
perpendiculars  through  the  point  of  intersection  will  indicate  on  either  of  the 
latter  the  joint-resistance  in  ohms. 


CIRCUITS  AND  CONDUCTORS 


85 


When  it  is  required  to  compute  the  joint-resistance  of  three  or  more 
conductors  as  in  Fig.  64  or  640,  the  same  formula  applies  as  in  the  case  of  a 
divided  circuit  having  two  branches.  First  the  joint-resistance  of  any  two 
of  the  branches  is  ascertained,  and  the  result  thus  obtained  combined  in  the 
same  way  with  another  of  the  conductors,  and  so  on  until  all  branches  have 
been  included  in  the  calculation.  To  illustrate,  suppose  that  in  Fig.  64,  RI 
has  a  resistance  of  40  ohms,  R<>,  50  ohms,  and  R3,  60  ohms,  then,  combining 
RI  and  R%  first,  we  have 

40X50 

—  :  -  =  22  2/9  ohms. 
40+50 


Combining  the  joint-resistance  of 
have 


and  R2  with  that  of  the  third  branch,  we 


R  = 


_22   2/9X60 


16+  ohms. 


22    2/9  +  60 

If  there  were  a  fourth  branch,  the  process  would  be  continued  in  the  same 
manner,  that  is,  the  joint  resistance  of  the  first  three  branches,  16+  ohms, 


FIG.  64. 


FIG.  640. 


would  be  combined  with  the  resistance  of  the  fourth  branch  as  above 
explained. 

The  graphic  method  illustrated  in  Fig.  63  also  may  be  used  to  determine 
the  joint-resistance  of  three  or  more  branches  of  a  divided  circuit.  The 
derived  perpendicular  indicating  the  joint-resistance  of  the  first  two  branches 
considered,  would  then  have  a  diagonal  drawn  from  its  upper  extremity 
intersecting  a  fourth  diagonal  representing  the  resistance  value  of  the  third 
wire,  and  so  on. 

Where  it  is  desired  to  determine  the  joint-resistance  of  a  large  number  of 
conductors  connected  in  parallel  it  will  facilitate  the  computation  to  employ 
the  rule: 

The  joint-resistance  of  any  number  of  conductors  in  parallel  is  the  reciprocal 
of  the  sum  of  the  reciprocals  of  the  separate  resistances. 

Figure  64  represents  a  derived  circuit  having  three  branches.  Let  RI, 
RZ,  and  RS  represent  the  respective  resistances  of  the  three  branches,  then 

j?->  XT*  and  -=-  are  the  separate  reciprocals  of  the  resistances  of  each 
KI  jci         ^3 

branch.     Therefore  the  joint-conductivity  would  equal 
i       i        i 

T>          '       TT>         I       T> 

-ft-l        A2        J\-3 


86  AMERICAN  TELEGRAPH  PRACTICE 

And,   as   the  joint-resistance  is   the  reciprocal   of   the  joint-conductivity, 


Therefore 


40X50X60 

K  =7  —  .  .  ,  \  .  ,  —  vx,  N  ,  ,  —  —  —  ^  =  io-h  onms, 
(50X60)  +  (40X60)  +  (40X50) 


or  the  same  result  as  was  obtained  by  the  first  method. 

Figure  640  shows  several  conductors  leading  from  a  source  of  e.m.f.  and 
placed  in  contact  with  the  earth  as  also  is  the  opposite  terminal  of  the  bat- 
tery. Electrical  circuits  arranged  in  this  way  are  termed  ground-return 
circuits,  while  the  arrangement  of  conductors  shown  in  Fig.  64  provides  what 
is  termed  a  metallic  circuit. 

In  telegraphic  practice,  the  earth  is  generally  availed  of  as  a  return 
conductor.  There  are  two  or  three  different  theories  held  pertaining  to  the 
part  which  the  earth  plays  in  completing  electrical  circuits,  but  so  far  as 
present  purposes  are  concerned  none  of  these  theories  are  of  practical  impor- 
tance. Suffice  it  that  for  ordinary  requirements  we  are  able  to  obtain  a 
complete  electrical  circuit  by  using  the  earth  as  a  part  of  circuits  otherwise 
made  up  of  metallic  conductors. 

Shunt  Circuits.  —  In  any  combination  of  branch  circuits,  each  branch  acts 
as  a  by-pass  for  a  portion  of  the  current,  and  any  branch  carrying  a  portion 

of  the  current  in  a  circuit  is,  in  effect,  a 

~P      |R  ^  shunt  to  the  other  branches  of  the  circuit  thus 
f         ^500 

divided.      There  are  instances  where  the  ap- 

plication of  a  shunt  circuit  requires  that  a 
FIG.  65.  definite  value  be  given  the  shunt  in  order  to 

regulate  the  amount  of  current  flowing  in  a 

branch  circuit  connected  in  parallel  therewith.     For  example,  suppose  it  is 
required  to  provide  a  shunt  "S,"  (Fig.  65,)  having  a  resistance  which  will 
permit  one-third  of  the  total  current  in  the  circuit  to  flow  through  the  500- 
ohmcoil  shown  on  the  right,  what  must  be  the  resistance  of  the  shunt? 
Let  R  represent  the  resistance  of  the  circuit  to  be  shunted, 
n  represent  the  multiplying  power  of  the  shunt, 
S  represent  the  resistance  of  the  shunt, 

Then  s_    R 

n—i 

The  value  of  n  is  arrived  at  when  it  is  known  what  proportion  of  the  current 
is  to  be  shunted.  In  the  case  before  us,  it  is  required  that  one-  third  of  the 
total  current  shall  pass  through  branch  R,  therefore  the  multiplying  power  is 
3,  and 

''•  '  500 

3-!=25°' 
5  =  250  ohms. 


FALL  OF  POTENTIAL 


87 


To  find  the  multiplying  power  of  a  shunt  of  known  resistance,  the  following 

formula  applies: 

R+S 


Suppose,  for  instance,  that  the  multiplying  power  in  the  former  example  is 
unknown,  and  it  is  desired  to  learn  the  current  proportions  in  each  branch  of 
the  circuit. 
Then 


and 


,5  =  250 
500+250 


250 


=  3* 


E.M.F.  120  Volts 


110' 
100 1 
90  i 
80. 
7d 
60  r 
50. 
40' 
30' 
20' 
10' 


1 


FIG.  66. — Fall  of  potential. 


Fall  of  Potential  in  an  Electric  Circuit. — Some  little  confusion  at  times 
results  from  the  use  interchangeably,  of  the  terms  electromotive  force  and 
potential  difference.  In  practice,  it  is  usual  to  regard  a  primary  battery, 
storage  battery,  dynamo-electric  machine,  or  other  generator  of  electricity  as 
having  a  definite  e.m.f.,  while  an  external  circuit  connected  to  the  terminals  of 
a  given  e.m.f.  will  have  a  difference  of  potential  which  decreases  in  value  as 
resistance  is  overcome,  in  a  direction  from  positive  to  negative  terminal  of 
the  source  of  e.m.f.  If  a  circuit  external  to  the  source  of  e.m.f.  consists  of  a 
single  conductor  of  uniform  composition  and  uniform  dimension  throughout, 
and  consequently  of  uniform  resistance;  it  is  found  that  the  potential  falls 
uniformly  in  a  direction  as  stated  above. 

When  a  current  flows  in  a  conductor  such  as  that  illustrated  by  the  heavy 
line  A-E,  Fig.  66,  the  difference  of  potential  between  the  conductor  and  the 
earth  at  E  decreases  in  the  direction  in  which  the  current  is  flowing.  If  a 


88  AMERICAN  TELEGRAPH  PRACTICE 

dotted  perpendicular  is  erected  at  the  battery  end  of  the  line  representing 
the  conductor;  the  height  of  the  perpendicular  representing  the  value  of  the 
e.m.f.  in  volts,  and  a  horizontal  line  is  drawn  from  the  top  of  the  former  as 
shown,  we  have  a  means  of  determining  the  difference  of  potential  between 
any  specified  point  along  the  conductor  and  the  earth. 

For  example,  if  it  is  desired  to  ascertain  the  difference  of  potential  between 
a  point  (C)  halfway  along  the  conductor,  and  the  earth,  the  erection  of  a 
perpendicular  at  that  point  between  the  base  line  and  the  dotted  horizontal 
will  indicate  the  difference  of  potential  in  volts  as  measured  by  an  identical 
height  of  the  perpendicular  at  the  end  of  the  base  line;  in  this  case,  60  volts. 
Obviously  the  difference  of  potential  between  any  point  along  the  conductor 
and  the  earth  may  be  determined  in  the  same  manner. 

160 c^ 

150 1       "\ 

140i  "x^ 

130,  *\ 

120 1 

1101  \ 

100. 

90i --i^ 

80 1 
70 1 
60. 
50 
40 1 
30> 
20' 
101 


FIG.  67.— Fall  of  potential. 

Consider  a  circuit  such  as  that  depicted  in  Fig.  67,  where  an  e.m.f.  of  160 
volts  is  applied  to  a  grounded  circuit  of  340  ohms  resistance,  and  it  is  desired 
to  ascertain  what  the  difference  of  potential  is  at  a  point  150  ohms  "distant" 
from  the  source  of  e.m.f.  If  the  distance  in  ohms  from  o  to  340  is  properly 
graduated  along  the  base  line  representing  the  conductor,  and  the  e.m.f.  in 
volts  properly  indicated  along  the  perpendicular  representing  e.m.f.,  then  a 
perpendicular  erected  at  that  point  on  the  base  line  indicating  150  ohms  will 
be  found  to  have  a  height  identical  with  the  height  of  the  perpendicular  repre- 
senting the  e.m.f.  at  a  point  which  indicates  90  volts,  approximately;  or,  to  be 
exact,  89.41  volts.  Obviously  the  difference  of  potential  at  any  point  along 
the  conductor,  distant  in  ohms  from  the  source  of  e.m.f.,  may  be  determined 
in  the  same  manner. 


FALL  OF  POTENTIAL  89 

The  above  graphical  method  of  determining  the  difference  of  potential  in 
a  circuit  while  of  considerable  value  in  clearly  setting  forth  the  principles  in- 
volved in  the  fall  of  potential,  is  seldom  used  in  practice.  A  formula  based 
on  Ohm's  law,  and  by  which  the  same  end  may  be  attained,  is  given  herewith: 

Where  E  represents  the  applied  e.m.f.,  in  volts, 

R  represents  the  resistance  in  ohms,  of  the  entire  circuit, 

Ri  represents  the  point  distant  in  ohms  from  the  source  of  e.m.f., 

where  the  value  of  the  difference  of  potential  is  desired, 
then 

X  = 


R 

Employing  this  formula  to  determine  the  difference  of  potential  at  a  point 
150  ohms  distant  from  the  source  of  e.m.f.  in  a  circuit  having  a  total  resistance 
of  340  ohms  (Fig.  67)  and  an  applied  e.m.f.  of  160  volts,  we  have, 

£=160 
^  =  340 

and 

i6oX(34Q-i5°) 
340 

_  160X190 
340 

X  =  —  -  =  89.41.  ans.,  89.41  volts,  or  the  same  as  was  determined  by  the 
graphic  method. 

ELECTROSTATIC  CAPACITY  OF  CONDUCTING  WIRES 

When,  as  "charge,"  electricity  is  present  upon  the  surface  of  bodies,  it  is 
referred  to  as  static  electricity.  In  the  operation  of  telegraph  lines,  static 
electricity,  is  encountered;  generally  as  a  disturbing  agency,  due  to  the  fact 
that  charge  is  accumulated  on  the  surface  of  the  conductor-  from  both  inter- 
nal and  external  sources. 

A  knowledge  of  the  principles  of  electrostatics  is  essential  in  the  study  of 
telegraphy,  and  while  it  is  true  that  the  subject  is  pretty  well  covered  in  text- 
books dealing  with  electricity  and  magnetism,  the  bearing  which  the  subject 
has  upon  practical  telegraphy  has  not  always  been  clear  to  the  student. 

If  one  end  of  a  telegraph  line  is  connected  with  one  terminal  of  a  source  of 
e.m.f.,  while  the  other  terminal  of  the  battery  and  the  other  end  of  the  line  are 
grounded  (Fig.  68)  it  may  be  shown  that  when  the  key  K  is  closed,  current 
traverses  the  entire  circuit  almost  instantaneously,  affecting  the  distant  end 


90 


AMERICAN  TELEGRAPH  PRACTICE 


of  the  conductor  at  nearly  the  same  instant  that  the  key  is  closed.  The  first 
indication  of  electrification  at  the  distant  end,  however,  is  quite  feeble,  but  the 
current  strength  increases  gradually  until  maximum  value  obtains.  If  a 
current-indicating  meter  be  inserted  at  the  distant  end  of  the  line,  there  will 
be  no  deflection  of  its  pointer  until  the  current  has  attained  a  strength  sufficient 
to  energize  the  coils  of  the  instrument  thereby  causing  the  indicating  needle 
to  move  from  its  position  of  rest.  The  more  sensitive  the  instrument  employed 
for  the  purpose,  the  earlier  will  be  the  indication  of  current  passing  through  it. 


K 


FIG.  68. 


1 


After  the  first  movement  of  the  needle  has  been  observed,  the  amount  of 
deflection  will  increase  gradually  until  when  maximum  current  obtains  at  the 
distant  end,  the  pointer  will  have  moved  to  a  definite  position,  distant  from  its 
position  of  rest.  On  short  lines  the  interval  elapsing  between  the  time  the  key 
is  closed  and  the  time  constant-current  is  indicated  is,  of  course,  very  brief. 
Should  several  current-indicating  instruments  be  inserted  at  different  points 
along  the  line  as  shown  in  Fig.  69,  when  the  key  is  closed  placing  the  source 
of  e.m.f.  in  contact  with  the  line,  the  instrument  nearest  the  battery  end  of  the 


<2>    CD 


FIG.  69. 

line  will  be  the  first  to  indicate  the  presence  of  current,  the  others  following 
in  order,  each  a  fraction  of  a  second  later  than  the  one  behind  it  until  the  in- 
dicator located  at  the  distant  end  of  the  line  is  affected. 

From  the  foregoing  it  is  apparent  that  current  does  not  arrive  at  the  distant 
end  of  a  line  "all  at  once"  as  does  a  bullet  at  a  target.  The  initial  portion  of 
current  flowing  into  a  conducting  wire  is  retained,  or  accumulated  on  the  sur- 
face of  the  conductor,  the  quantity  accumulated  depending  upon  the  length 
and  surface  of  the  wire,  upon  its  distance  from  the  surface  of  the  earth,  and 
upon  the  nature  of  the  dielectric  intervening  between  the  conductor  and 
the  earth. 

It  is  convenient  to  assume  that  the  conducting  wire  absorbs  the  first  portion 
of  each  charge  sent  into  it,  and  that  its  capacity  of  absorbing  electric  charge 
has  to  be  satisfied  before  constant  current  conditions  obtain  in  the  circuit  of 


ELECTROSTATIC  CAPACITY  OF  LINES  91 

which  the  conducting  wire  forms  a  part.  The  effect  is  as  if  the  conductor 
requires  to  be  "saturated"  before  delivering  current  at  the  distant  end  of  the 
line,  in  a  somewhat  similar  manner  to  that  of  a  sponge,  which  has  to  be  satu- 
rated to  capacity  before  water  drips  from  it. 

It  is  found  that  when  a  circuit,  such  as  that  shown  in  Fig.  69,  is  closed  by 
means  of  a  key  or  otherwise,  the  indicating  needles  of  the  instruments  located  on 
the  half  of  the  line  nearest  the  source  of  e.m.f.  "  over-shoot "  the  point  at  which 
they  finally  come  to  rest,  while  the  indicating  needles  of  the  instruments  located 
on  the  other  half  of  the  line  have  a  continuously  increasing  angle  of  deflection 
until  the  conductor  has  become  fully  charged  and  normal  current  prevails,  at 
which  instant  the  needle  has  reached  its  maximum  deflection  and  remains  there. 
The  conditions  which  obtain  during  the  time  the  current  is  equalizing  through- 
out the  entire  circuit  is  referred  to  as  the  variable  state.  The  duration  of  the 
variable  state  varies  in  different  circuits  and  depends  upon  the  physical  and 
electrical  characteristics  obtaining  in  any  given  instance.1 

The  permanent  state  has  been  established  in  a  circuit  when  the  current 
strength  has  been  equalized  in  the  conducting  wire,  or  when  the  current  value 
has  become  constant.  The  permanent  state  is  first  established  in  the  middle 
of  the  line,  at  an  instant  practically  four  times  sooner  than  constant-current 
conditions  prevail  at  either  end  of  the  line.  The  statement  that  the  "  quantity 
of  charge  accumulated  on  the  surface  of  a  conducting  wire,  depends  upon  the 
dielectric  intervening  between  the  conductor  and  the  earth,"  in  so  far  as  aerial 
lines  are  concerned,  involves  an  understanding  of  the  conditions  prevailing  at 
all  points  along  the  length  of  the  conductor.  When  properly  suspended  and 
insulated,  the  conductor  is  enveloped  in  aji  insulating  stratum  of  air,  but  this 
stratum  varies  in  thickness  as  the  conductor  is  carried  past  objects  which  are  in 
contact  with  the  earth. 

As  the  surface  of  a  conducting  wire  increases  with  its  radius,  the  inductive 
capacity  of  the  wire  increases  proportionately.  The  greater  the  inductive  or 
electrostatic  capacity  of  a  conducting  wire,  the  longer  time  it  takes  to  charge  it 
—the  longer  the  duration  of  its  variable  state. 

The  electrostatic  capacity  of  a  conducting  wire  in  effect  diminishes  the 
velocity  of  electrical  action  along  the  conductor,  that  is,  each  time  the  circuit 
is  closed  through  a  source  of  e.m.f.  electrostatic  capacity  has  the  effect  of 
retarding  or  delaying  the  initial  appearance  of  current  at  the  distant  end  of  the 
wire. 

In  the  transmission  of  telegraph  signals  over  a  wire,  the  circuit  is  closed  and 
opened,  say,  four  or  five  times  per  second,  and  in  the  case  of  long  lines,  the 
effect  of  electrostatic  capacity  is  to  considerably  curtail  the  number  of  impulses 
or  signals  which  may  be  sent  over  the  wire  in  a  given  time.  Where  slow  signal- 

1  A  further  treatment  of  the  subject  of  capacity  is  given  in  Chapter  X  in  con- 
nection with  electric  condensers,  and  in  Chapter  XI  dealing  with  "Speed  of  Signal- 
ing," also  see  "The  Capacity  Balance,"  Chapter  XV. 


92  AMERICAN  TELEGRAPH  PRACTICE 

ing  is  concerned  the  effects  of  capacity  are  not  of  much  consequence,  but  where 
high  speeds  are  concerned  the  electrostatic  capacity  of  a  circuit  may  be  the 
criterion  of  speed  attainable. 

Electrostatic  Induction. — Where  a  charge  of  electricity  of  either  sign 
(positive  or  negative)  exists  on  a  conductor,  it  will  induce  in  neighboring 
conductors  a  bound  static-charge  of  opposite  sign  on  that  side  of  the  adjacent 
wires  nearest  to  it  and  a  charge  of  identical  sign  on  the  sides  farthest  away 
from  it.  See  Fig.  6ga. 

+  +H-+    -h    +.  +  +  -f  4-  + 


FIG.  6ga. — Electrostatic  induction. 

The  upper  conductor  is  represented  as  having  a  positive  charge  and  the 
interaction  which  takes  place  between  the  upper  and  the  lower  wires  results 
in  a  bound  negative  charge  being  induced  on  the  upper  surface  of  the  lower 
wire,  while  on  the  under  side  of  the  latter  a  free  positive  charge  will  appear. 
If  the  current  in  the  upper  wire  should  be  changed  from  positive  to  negative, 
the  reverse  process  would  take  place  in  the  lower  wire;  thus,  if  the  direction  of 
current  in  the  upper  conductor  is  alternated  from  positive  to  negative  and 
back  again  either  slowly  or  rapidly  a  continuous  interaction  takes  place  be- 
tween the  upper  and  lower  conductors. 

Electromagnetic  Induction. — Any  conducting  wire  charged  with  current 
has  surrounding  it  at  all  points  along  its  length,  lines  of  force  in  the  form  of 
closed  rings  or  loops,  and  the  space  surrounding  a  charged  conducting  wire  is 


B 


D 


FIG.  70.  FIG.  71. 

an  active  magnetic  field.  As  will  be  described  later  in  connection  with  the 
theory  of  electromagnetism,  current  in  a  circuit  while  increasing  or  decreasing 
in  strength  exercises  an  inductive  effect  upon  neighboring  circuits.  It  is  true 
also  that  due  to  the  expansion  and  contraction  of  the  magnetic  rings  surround- 
ing the  conductor,  as  the  circuit  is  closed  and  opened,  there  is  an  inductive 
action  of  the  current  in  the  conductor  upon  itself.  Naturally  this  effect  of 
self-induction  is  great  if  the  circuit  (as  in  the  case  of  magnet  coils)  is  made  up 
of  a  coil  of  many  convolutions,  and  much  greater  still  when  the  turns  of  wire 
surround  an  iron  core.  If  a  current  is  caused  to  flow  in  the  wire  A-B, 
Fig.  70,  in  the  direction  indicated  by  the  arrow,  commencement  of  cur- 
rent or  increase  in  its  strength  induces  a  current  in  the  neighboring  con- 


ELECTROMAGNETIC  INDUCTION  93 

ductor  C-D  in  the  direction  indicated,  or  the  reverse  of  the  direction  of  current 
in  the  inducing  circuit.  In  a  circuit  such  as  that  shown  in  Fig.  71  where  the 
conducting  wire  is  coiled  back  upon  itself,  an  increasing  current  flowing  in  the 
direction  A-B  in  the  outer  convolution,  induces  a  current  to  flow,  or  to  attempt 
to  flow  in  the  opposite  direction  C-D.  The  induced  current  being  greatly 
inferior  to  the  original  current  in  strength,  results  only  in  opposing  the  latter 
and  delaying  its  rise  to  maximum  strength.  When  the  circuit  is  opened  and 
the  current  strength  in  that  portion  of  the  circuit  A-B  is  decreasing,  it  tends 
to  induce  a  current  between  C  and  D  in  the  same  direction  as  that  of  the  origi- 
nal current,  and  this  results  in  prolonging  the  duration  of  the  latter  by  virtue 
of  the  induced  opposition  to  its  decrease.  In  either  case  the  effect  of  self- 
induction  is  to  oppose  change,  and  in  a  sense  might  be  regarded  as  electro- 
magnetic inertia.  The  fact  that  individual  impulses  are  thus  in  turn  retarded 
and  prolonged  diminishes  the  rate  at  which  signals  may  be  sent  over  long  lines, 
as  fewer  distinct  impulses  can  be  transmitted  in  a  given  time. 

In  comparison  with  the  effects  of  electrostatic  induction,  the  effects  of 
electromagnetic  induction  in  lines  of  ordinary  lengths  is  very  slight.  In  very 
long  lines  the  reverse  is  sometimes  true.  Where  magnet  coils  are  concerned, 
such  as  are  essential  in  terminal  apparatus,  self-induction  plays  a  prominent 
part  in  limiting  the  speed  of  operation  over  a  given  line,  and  in  limiting  the 
length  of  line  over  which  satisfactory  operation  may  be  maintained. 

The  length  of  time  required  for  an  impulse  to  reach  the  distant  end  of  a 
line  and  rise  to  a  strength  sufficient  to  operate  receiving  apparatus,  particu- 
larly electromagnetic  devices,  depends  upon  the  distributed  electrostatic 
capacity  and  the  ohmic  resistance  of  the  circuit.  In  fact,  it  has  been  deemed 
good  practice  to  consider  that  the  limits  of  satisfactory  operation  are  pro- 
portional to  the  product  of  these  two  factors,  which  would  mean  that  the  prod- 
uct should  be  kept  at  as  low  a  figure  as  practicable. 

The  electrostatic  capacity  of  aerial  conductors  suspended  at  any  height 
above  the  surface  of  the  earth  is  intricately  involved  with  the  number  of 
and  relative  proximity  of  other  wires  on  the  same  pole  line.  A  single  No.  12 
B.  &  S.  gage  copper  wire  suspended  30  ft.  above  the  earth,  with  both  ends 
grounded,  was  in  one  instance  found  to  have  a  capacity  of  0.009379  micro- 
farads per  mile  and  an  inductance  of  0.003149  henries  per  mile.  Two  similar 
wires  placed  i  ft.  apart  and  suspended  30  ft.  above  the  earth  were  found  to 
have  a  capacity  between  either  wire  and  the  earth  of  0.012  microfarad  per 
mile.  For  a  line  500  miles  long  this  would  mean  a  total  capacity  of  6 
microfarads. 

It  is  important  to  note  the  difference  in  the  interactions  taking  place  be- 
tween neighboring  conductors,  attributable  to  electromagnetic  induction  and 
to  electrostatic  induction. 

Figure  72  gives  a  cross-section  or  end-view  of  two  conducting  wires  carrying 
current.  The  closed  loops  shown  perpendicular  to  and  surrounding  each 


94 


AMERICAN  TELEGRAPH  PRACTICE 


conducting  wire  represent  the  magnetic  rings  which  exist  during  the  periods 
that  current  is  flowing  in  either  direction  through  a  conductor.  If  we  sup- 
pose a  condition  such  as  that  shown  in  Fig.  73  where  current  is  temporarily 
suspended  in  one  wire  while  current  in  the  other  wire  is  increasing  or  decreas- 
ing in  strength,  a  current  will  be  induced  in  the  wire  B  due  to  its  cutting  the 
expanding  and  contracting  magnetic  rings,  as  they  are  called  into  being  or 
destroyed,  by  the  closing  or  opening  of  the  circuit  of  which  wire  A  forms  apart. 
As  we  proceed  with  the  study  of  the  various  factors  which  have  a  bearing 
on  the  current  strength  in  electrical  circuits,  it  becomes  apparent  that  Ohm's 
law,  strictly  speaking,  is  not  applicable  except  where  the  factors  are  constant. 


FIG.  72.  FIG.  73. 

FIGS.  72  and  73.  —  Electromagnetic  induction. 

At  the  outset  it  is  apparent  that  when  a  current  of  electricity  is  turned  into  a 
circuit  for  a  brief  instant  and  then  interrupted,  or  when  a  circuit  is  first 
closed  through  a  source  of  e.m.f.,  the  current  strength  in  the  circuit  for  a 
short  period  is  not  truly  represented  by  the  formula 


From  what  has  been  stated  in  regard  to  the  effects  of  capacity  and  induc- 
tance in  electric  circuits,  it  is  evident  that  the  factor  of  "time"  plays  an 
important  part  in  determining  the  current  strength  obtaining  in  a  given 
circuit  at  a  given  instant. 

Pulsatory  currents  of  either  polarity  or  currents  which  alternate  in  direc- 
tion do  not  have  a  value  in  accordance  with  Ohm's  law. 

Helmholtz  the  great  German  physicist  interpreted  Ohm's  law  in  a  form 
which  takes  into  consideration,  the  element  of  "time"  and  from  this  evolved 


ELECTROMAGNETIC  INDUCTION  95 

a  formula  which  gives  the  current  value  in  a  circuit  at  any  given  instant,  thus, 

Rt\ 

~L) 

I-e   I 

Where  /,  is  the  current  in  amperes, 

£,  is  the  applied  e.m.f., 

R,  is  the  resistance  in  ohms, 

t,    is  the  time  in  seconds, 

L,  is  the  inductance  in  henries, 

e,  is  the  base  of  the  system  of  natural  logarithms,  or  2.7183. 
In  telegraph  circuits  operated  at  usual  speed,  it  is  obvious  that  the  low  value 
of  the  negative  exponent  in  the  above  formula  would  give  a  determination 
practically  agreeing  with  that  obtained  by  means  of  Ohm's  law,  but  if  the 
value  of  /  is  reduced  or  the  value  of  L  is  increased,  a  point  is  soon  reached 
where  the  simpler  law  would  not  give  a  true  indication  of  the  condition. 

The  electrical  properties  as  well  as  the  physical  properties  of  a  circuit 
may  be  determined  without  regard  to  the  e.m.f.  to  be  applied  to  it.  A  tele- 
graph circuit,  including  as  it  does  the  magnet  winding  of  receiving  in- 
struments, offers  a  greater  resistance  to  the  passage  of  currents  which  alter- 
nate in  polarity  than  is  represented  by  the  resistance  of  the  circuit  in  ohms, 
the  additional  resistance  being  the  direct  result  of  inductance.  The  resist- 
ance in  ohms  combined  with  the  inductance  in  henries  produces  impedance 
(symbol  Z). 

If  L  =  the  inductance  in  henries,1 
N  =  cycles  per  second, 
R  =  the  resistance  in  ohms, 
then 


Current  in  amperes 

e.m.f. 


impedance 
Assume  a  circuit  having  values  as  follows: 
R=  1,200  ohms, 
N=      20  cycles  per  second, 
L=        6  henries. 

By  means  of  the  above  formula  the  impedance  (Z)  may  be  shown  to  be  1,417, 
and  the  maximum  current  to  be  141  milliamperes,  where  an  e.m.f.  of  200 
volts  is  applied  to  the  circuit;  while  Ohm's  law 


1  A  definition  of  the  value  of  the  henry  is  given  in  Chapter  I,  and  a  method  of  measuring 
inductance  is  described  on  page  103. 


96  AMERICAN  TELEGRAPH  PRACTICE 

would  give  the  current  value  as  167  milliamperes.  Thus  by  considering 
frequency  and  inductance  as  factors,  in  the  same  sense  that  resistance  is 
considered,  it  is  possible  to  arrive  at  the  true  value  of  the  current  flowing 
in  the  circuit. 

ELECTROMAGNETISM  AND  ELECTROMAGNETS 

The  phenomenon  of  magnetism  may  be  exhibited  by  bringing  a  piece  of 
iron  into  the  neighborhood  of  a  natural  magnet  (lodestone),  permanent 
magnet  or  any  form  of  electromagnet,  where  it  may  be  attracted.  If  free 
to  move,  the  iron  will  come  into  contact  with  and  cling  to  the  magnet.  A 
powerful  magnet  will  have  an  appreciable  effect  upon  a  delicately  poised 
needle  (see  Fig.  74)  even  if  the  two  are  situated  a  considerable  distance 

apart,  and  undoubtedly  the  influence  of 
the  magnet  extends  far  beyond  the 
boundary  established  by  the  methods 
ordinarily  employed  to  determine  its 
range. 

It  is  customary  to  consider  iron  as 
being  peculiarly  subject  to  magnetic 
influence,  and  as  stated  in  the  chapter 

on   Electricity  and   Magnetism,    steel, 
FIG.  74.— Compass  needle  deflected  by       ... 

the  influence  of  a  horseshoe  magnet.        mckel>    cobalt>    chromium,    manganese 

and  other  substances  are  similarly  in- 
fluenced to  an  extent  varying  in  the  case  of  each  substance. 

Also  it  is  known  that  all  kinds  of  matter  possess  this  magnetic  quality  in 
some  degree.  It  has  been  shown  experimentally  that  temperature  plays 
an  important  part  in  determining  the  magnetic  susceptibility  of  a  substance. 
Iron,  for  instance,  when  heated  to  750°  is  irresponsive  to  magnetic  influence, 
the  reason,  roughly  stated,  being  that  the  atomic  structure  of  the  substance 
is  so  disarranged  by  high  temperature  that  the  atoms  are  unable  to  "line-up" 
magnetically  in  response  to  the  influence  of  the  inducing  magnet. 

Although  for  present  purposes  (investigating  the  properties  of  electric 
circuits),  we  may  acquire  the  desired  information  relating  to  the  magnetic 
properties  of  conductors  carrying  currents  of  electricity,  by  studying  the 
magnetic  action  of  solenoids,  the  further  study  of  electromagnets  requires 
that  the  connecting  link  between  the  two — the  core — be  treated  of  at  the 
same  time,  or  in  connection  therewith. 

A  helix  of  wire  carrying  a  current  of  electricity  possesses  magnetic  proper- 
ties. When  the  helix  consists  of  a  coil  of  insulated  wire  and  is  wound  around 
a  bar  of  soft  iron,  the  iron  becomes  magnetized  when  the  electric  circuit  is 
energized,  and  the  combination  of  helix  and  core  is  called  an  electromagnet. 
Substances  in  which  a  magnetizing  force  produces  a  high  degree  of  magneti- 
zation, are  regarded  as  possessing  high  permeability. 


ELECTRON  AGNETISM 


97 


The  intensity  of  magnetization,  while  in  part  dependent  upon  the  strength 
of  magnetic  field  produced  by  the  helix,  is  also  dependent  upon  the  properties 
of  the  metal  forming  the  core,  that  is,  upon  its  permeability. 

If  a  conducting  wire  connected  through  a  source  of  e.m.f.  is  bent  into  a 
loop  as  in  Fig.  75  the  lines  of  force  will  thread  through  the  loop  from  one  end 
to  the  other  in  a  direction  depending  upon  the  direction  in  which  the  current 
is  flowing  through  the  conducting  wire.  Should  an  iron  core  M  be  brought 
close  to  the  loop  of  wire  thus  formed,  the  core  would  tend  to  enter  the  loop 
lengthwise,  that  is,  place  itself 
with  its  longest  axis  projecting 
into  the  loop  of  wire,  and  always 
in  a  direction  the  same  as  that 
taken  by  the  lines  of  force.  If 
the  conducting  wire  is  coiled  into 
a  helix  or  solenoid  having  a  num- 
ber of  loops,  as  in  Fig.  76,  the 
lines  of  force  around  each  turn  or 
loop  will  reinforce  those  around 
neighboring  loops,  and  the  cumu- 
lative result  will  be  the  formation 
of  numerous  long  lines  of  force 
as  shown,  which  extend  through  the  entire  coil. 

The  above  statements  mean  that  the  solenoid  possesses  properties  iden- 
tical with  those  possessed  by  bar  magnets  (permanent  magnets).  Inasmuch 
as  the  lines  of  force  enter  one  extremity  and  leave  at  the  other,  the  solenoid 
exhibits  the  phenomenon  of  polarity,  having  a  north  and  a  south  pole.  A 


FIG.  75. — Direction  of  current  in  a  completed 
circuit  and  resulting  lines  of  force. 


FIG.  76. — The  solenoid. 

coil  such  as  that  shown  in  Fig.  76  if  traversed  by  an  electric  current,  and 
suspended  in  a  horizontal  position,  will,  if  free  to  turn,  come  to  rest  pointing 
in  a  north  and  south  direction. 

The  polarity  of  a  solenoid  is  dependent  upon  the  direction  in  which  a 
current  of  electricity  flows  through  it,  and  upon  the  direction  in  which  the 
conducting  wire  is  wound  in  forming  the  coil.  The  presence  of  an  iron  core 
very  greatly  increases  the  number  of  lines  of  force  passing  through  the  coil 
from  end  to  end,  the  amount  of  increase  being  dependent  upon  the  permea- 
bility of  the  substance  forming  the  core.  Obviously,  when  no  core  is  inserted 


98  AMERICAN  TELEGRAPH  PRACTICE 

in  the  coil  there  is  a  considerable  amount  of  leakage  of  the  lines  of  force  out 
through  the  sides  of  the  coil  as  indicated  in  Fig.  76,  the  total  number  extend- 
ing all  the  way  through  being  small  compared  with  the  number  of  lines 
carried  to  the  polar  extremities  due  to  the  concentrating  properties  of  the 
iron  core.  In  fact,  the  presence  of  a  core  not  only  reduces  the  leakage  of 
lines  of  force  but  adds  materially  to  those  already  existing. 

(n 

As  was  stated  on  page  9,  permeability  (/*)  equals  ^ 

where  £B  represents  the  magnetic  induction  in  lines  of  force  per  unit  area 

of  cross-section, 
^represents  magnetizing  force. 

Permeability. — Permeability  might  be  referred  to  as  that  characteristic 
susceptible  of  expression  through  a  numerical  coefficient  representing  the 
ratio  between  the  number  of  lines  of  force  formed  in  a  space  containing  air 
only,  as  in  Fig.  76,  and  the  number  of  lines  formed  in  a  space  filled  with  a 


FIG.  77.— The  electromagnet. 

given  quality  of  iron  as  in  Fig.  77.  This  ratio  varies  somewhat  with 
different  grades  of  iron  and  steel. 

Magnetic  resistance,  or  reluctance  («^),  is  less,  the  higher  the  coefficient 
of  permeability,  and,  naturally  the  higher  the  permeability  of  a  substance, 
the  better  it  is  suited  for  the  purposes  of  electromagnet  cores. 

On  page  25  the  relative  merits  of  various  grades  of  iron  and  steel  for 
field  magnet  core  purposes  were  given  in  the  order  of  their  permeability; 
to  these  might  be  added  silicon-steel,  as  the  latter  has  been  found  to  possess 
a  high  permeability  and  is  being  used  to  some  extent  in  the  manufacture  of 
magnet  cores. 

The  number  of  magnetic  lines  of  force  that  can  be  forced  through  a  core 
of  given  cross-section,  while  in  great  measure  dependent  upon  the  permea- 
bility of  the  substance  of  which  the  core  is  made,  also  has  to  do  with  the  degree 
of  magnetic  saturation  attainable  with  a  given  core  material  with  given  ex- 
citation, or,  in  other  words,  increasing  the  excitation  beyond  a  certain  point 
does  not  always  increase  the  number  of  line?  of  force.  In  each  case  a  point 
is  reached  beyond  which  there  will  be  no  increase  of  lines. 

A  specimen  of  iron  when  subjected  to  a  magnetizing  force  (£B)  capable 
of  producing,  in  air,  52  magnetic  lines  to  the  square  centimeter,  was  found 
to  contain  about  17,000  lines  per  square  centimeter.  By  means  of  the  for- 

(T> 

mula  /*=  ~'  the  permeability  in  this  instance  would  be  326  times  that  of  air. 


ELECTROMAGNETISM  99 

Good  grades  of  wrought  iron  will  carry  approximately  20,000  lines  per 
square  centimeter,  and  cast  iron  about  12,000  lines.  Figures  considerably 
higher  than  these  have  been  obtained  where  extraordinary  magnetizing 
forces  have  been  employed,  but  correctly  plotted  magnetization  curves 
show  that  there  are  pronounced  evidences  of  saturation  when  the  values 
reach  those  above  stated.  It  will  be  remembered  that  the  value  of  £B  is 
given  in  gausses,  the  definition  of  the  unit  being  stated  on  page  8. 

The  following  table  of  values  of  5H  and  <5#  from  samples  of  first  grade 
American  wrought  iron,  were  determined  by  Dr.  Sheldon,  and  the  magnetic 
permeability  in  each  case  may  be  ascertained  by  means  of  the  above  formula: 

7<  & 

(Gausses) 

10 13,00° 

20 14,70° 

30 15,300 

40 15,700 

50 16,000 

60 16,300 

70 ,  16,500 

80 16,700 

90 16,900 

100 17,200 

150 18,000 

2OO l8,7OO 

250 19,200 

300 > 19,700 

The  magnetomotive  force  or  magnetization  of  an  electromagnet  is  pro- 
portional to  the  number  of  turns  of  wire  wound  around  the  core,  and  the 
current  in  amperes  flowing  through  the  coil. 

A  unit  pole  will  have  4X3.1416  lines  of  force  proceeding  from  it,  or  to 
reduce  to  c.g.s.,  units 

47T 

—  =1.25764,  which  is  generally  taken  at  the  value  of  1.257. 

Where  TV  =  the  number  of  turns  in  the  coil, 

/  =  the  current  in  amperes. 
Magnetomotive  force  &  (Gilberts) 

=  1.257X^X1. 

A  field  of  ^  units  refers  to  one  where  there  are  3(  dynes  on  unit  pole,  and 
it  is  customary  to  follow  the  rule  of  drawing  a  number  of  lines  of  force  to 
the  square  centimeter  of  cross-section  of  the  core  equal  to  the  number  of 
dynes  of  force  on  the  unit  pole. 

Unit  of  Work. — The  unit  of  work,  the  erg,  refers  to  the  amount  of  work 
done  when  a  force  of  i  dyne  is  overcome  through  a  distance  of  i  cm.,  or,  in 
other  words,  the  amount  of  work  done  in  moving  a  body  through  a  distance 
of  i  cm.  against  a  force  of  i  dyne. 


100  AMERICAN  TELEGRAPH  PRACTICE 

A  unit  magnetic  pole  has  as  many  lines  of  force  proceeding  from  it  as  there 
are  square  centimeters  on  the  surface  of  a  sphere  of  i  cm.  radius.  A  sphere 
having  a  radius  of  2  cm.,  obviously  has  a  diameter  of  4  cm.,  and  an  area  of 
D2  X 3. 141 6.  A  sphere  having  a  radius  of  i  cm.  has  a  surface  area  of 
22  X3.i4I6  =  i2.5664  sq.  cm.,  therefore,  unit  magnet  pole  of  unit  strength 
has  12.5664  magnetic  lines  of  force. 

As  i  sq.  in.  is  equal  to  6.452  sq.  em.,  it  follows  that  when  unit  density  of 
magnetism  concerns  a  density  of  i  magnetic  line  of  force  per  square  centi- 
meter, we  have  an  equivalent  value  of  6.452  lines  per  square  inch  as  unit 
density  of  magnetism.  In  a  magnetic  circuit,  magnetomotive  force  corre- 
sponds to  electromotive  force  in  an  electric  circuit.  Reluctance,  or  mag- 
netic resistance  in  a  magnetic  circuit  corresponds  to  ohmic  resistance  in  an 
electric  circuit,  or 

magnetomotive  force 
Flux  =—  — 

reluctance 

Magnetic  flux  (The  Maxwell,  Symbol  0)  is,  therefore,  dependent  upon 
magnetic  reluctance  (The  oersted,  symbol  &}  the  latter  being  a  property 
which  tends  to  oppose  the  passage  of  magnetic  flux.  As  previously  stated, 
however,  the  magnetomotive  force  may  be  measured  in  terms  of  ampere- 
turns  (the  ampere- turn  is  equal  to  1.26  Gilberts). 

Hysteresis. — When  the  iron  or  steel  core  of  an  electromagnet  has  been 
magnetized  by  a  current  of  electricity  flowing  through  the  magnet  winding, 
and  the  exciting  current  is  discontinued,  the  core  will  be  found  to  retain 
more  or  less  magnetism.  The  magnetism  remaining  is  termed  residual,  and 
its  value  is  spoken  of  as  remanence. 

A  completely  closed  magnetic  circuit,  that  is,  one  where  the (( keeper"  or  ar- 
mature is  in  mechanical  contact  with  the  pole-faces  of  the  magnet,  will  show 
much  greater  remanence  than  one  having  an  air  gap  between  the  armature  and 
the  polar  extremities  of  the  magnet.  When  an  electromagnet  is  permitted 
to  draw  its  armature  into  actual  contact  with  its  pole-faces,  the  armature 
will  not  fall  back  instantly  when  the  exciting  current  is  discontinued,  due  to 
the  fact  that  it  is  held  fast  by  the  residual  magnetism  of  the  cores.  It  is 
for  the  purpose  of  avoiding  this  that  electromagnets  are  generally  so  arranged 
with  regard  to  the  moving  element — the  armature — that  mechanical  contact 
between  the  armature  and  the  pole-faces  does  not  occur  in  practice. 

It  is  common  practice  to  set  a  small  brass  pin  in  the  face  of  each  magnet 
pole,  the  pin  projecting  about  one-sixteenth  of  an  inch,  or  a  distance  suf- 
ficient to  prevent  the  armature  from  coming  into  actual  contact  with  the 
pole-faces  proper. 

The  brass  pin  is  really  a  safety  stop,  as  receiving  instruments  used  in 
telegraphy,  which  consist  mainly  of  an  electromagnet  and  an  armature  are 
so  designed  that  the  armature  "plays"  between  a  front  and  a  back  ''contact, " 


TIME-CONSTANT  101 

both  adjustable,  and  which  limit  the  travel  of  the  armature  within  any 
desired  space . 

Magnetic  materials  manifest  a  tendency  to  resist  any  change — either 
increase  or  decrease — in  their  magnetic  condition,  a  characteristic  which 
might  be  regarded  as  a  sort  of  magnetic  inertia,  and  which  is  known  as 
hysteresis. 

An  effect  of  hysteresis  is  to  cause  a  delay,  or  "lag"  in  the  magnetization 
of  the  core,  behind  the  energizing  current  traversing  the  winding  of  the 
magnet.  When  a  circuit  including  an  electromagnet  is  closed,  the  relation 
between  the  exciting  current  and  the  magnetic  flux  produced  will  be  such 
that  maximum  magnetization  will  lag  somewhat  behind  the  maximum  elec- 
trical excitation  of  the  winding.  The  result  being  that  there  will  be  a  time 
interval  of  a  fraction  of  a  second  between  the  time  the  electrical  circuit  is 
closed,  and  the  time  maximum  magnetic  flux  is  produced. 

A  part  only  of  this  delay  is  chargeable  to  hysteresis,  for,  as  was  pointed 
out  in  connection  with  the  effects  of  self-induction,  the  latter  phenomenon 
is  directly  responsible  for  the  delay  observed  in  the  increase  and  decrease  of 
electric  current  in  the  coil  winding,  which  in  turn  delays  the  increase  and 
decrease  of  magnetization  of  the  core. 

Time -constant. — When  a  constant  e.m.f.  is  impressed  on  a  circuit  includ- 
ing a  magnet  coil  possessing  inductance,  the  current  flowing  in  the  circuit 
does  not  reach  its  full  value  instantly,  as  at  first  it  is  opposed  by  the  counter 
electromotive  force  due  to  inductance.  The  counter  e.m.f.  gradually 
becomes  less  as  the  current  value  reaches  full  strength.  In  practice 
it  is  usual  to  regard  the  operating  requirements  as  such  that  a  value  of 
63.2  per  cent,  of  the  full  strength  of  the  current  should  obtain  in  an  efficiently 
operative  circuit.  The  period  required  to  attain  this  value  is  called  the 
time-constant  of  the  circuit. 

,.  ,  ,     inductance  (in  henries) 

Time-constant  (in  seconds)  = r-r      —7-. r — \ — » 

resistance  (in  ohms) 

or 

_  he nriesX  final  amperes 
applied  volts 

As  usually  submitted  the  first  formula  is  given  as 

Time-constant  =  ^  * 
K 

Suppose  for  example  that  it  is  desired  to  determine  the  time-constant  of  a 
relay  having  a  resistance  of  300  ohms,  and  an  inductance  of  2.65  henries. 
For  L  we  have  a  value  of  .265  and  for  R  a  value  of  300,  and 

2.65 


=  0.000, 

300 


or  a  time-constant  of  0.009  second. 


102  AMERICAN  TELEGRAPH  PRACTICE 

Assume  a  circuit  including  an  electromagnet  to  have  a  resistance  of 
600  ohms  and  an  inductance  of  6  henries,  then  with  an  e.m.f.  of  40  volts 
applied  to  the  circuit  the  time-constant  would  be 

T — =0.01  (second). 
600 

By  means  of  the  formula 

I  =  ^r>>  the  final  current  strength  in  the  circuit 


would  be 

40 


600 


=  0.066  ampere, 


therefore  in  o.oi  second  the  current  strength  in  the  circuit  will  have  reached 
a  value  of  0.041  ampere,  or  0.632  of  its  full  strength. 

The  same  result  could  have  been  obtained  by  means  of  the  second  formula, 
or 

Tf 

Time-constant  —L- 


E 

6X40 

=  —        ^40  =  0.01  second. 
600 

The  several  electrical  and  mechanical  actions  which  govern  the  forward 
and  backward  movement  of  the  armature  of  a  telegraph  relay,  thus  are 
involved  with  the  element  of  time,  even  if  but  a  fraction  of  a  second  is 
consumed  with  each  transit.  The  time-constant,  therefore,  of  the  circuit 
refers  to  the  time  in  seconds,  or  fractions  thereof,  which  it  takes  the  current 
strength  in  the  circuit  to  build  up  to  a  value  approximately  two-thirds  that 
of  its  final  strength.  On  the  other  hand,  after  the  armature  has  been 
attracted  toward  the  pole-faces  of  the  magnet,  and  the  circuit  again  opened 
or  discontinued,  it  requires  an  appreciable  time  for  the  magnet  to  "let  go" 
the  armature  or  to  release  it.  Careful  experiments  have  shown  that  after 
the  magnet  circuit  has  been  opened,  the  average  time  required  for  a  magnet 
to  release  its  armature  varies  from  0.003  seconds  with  maximum  retractile 
spring  tension  to  0.033  with  minimum  retractile  tension.  Average  opera- 
ting adjustments  obviously  give  "releasing"  values  about  midway  between 
these  figures. 

In  determining  the  time-constant  of  a  circuit  which  includes  electro- 
magnets by  either  of  the  above  formulae,  it  is  required  that  the  inductance 
be  known.  In  cases  where  the  impressed  electromotive  force  varies  according 


TIME-CONSTANT  103 

to  the  Sine  law  of  alternating  currents  and  the  inductance  (L)  is  constant, 
the  effective  value  of  the  inductive  counter  e.m.f.  is 

E  =  27T  fLI,  where 

/  represents  "  frequency"  or  cycles  per  second, 

7  the  effective  value  of  the  current, 
E  would  then  be  the  inductive  reactance,  or  the  inductance  of  the  circuit. 

Another  method,  and  one  more  applicable  in  approximating  the  induc- 
tance of  magnets  used  for  telegraphic  purposes,  is  that  known  as  the  "  standard 
condenser"  method. 

By  means  of  a  Wheatstone  bridge  and  an  adjustable  condenser  arranged 
as  shown  in  Fig.  78,  the  inductance  of  a  magnet,  a  pair  of  magnets,  or  an 
"  instrument"  may  be  determined  quite  accurately. 

The  four  arms  of  the  bridge,  namely,  a,  b,  x,  and  R,  are  shown  in  their 
respective  positions.  G  is  a  galvanometer,  r  an  adjustable  resistance,  and 
C  an  adjustable  condenser.1 

The  "  instrument"  to  be  measured  for  inductance  is  inserted  at  X, 
then,  after  the  bridge  has  been  balanced;  that  is,  after  R  has  been  ad- 
justed to  equal  the  resistance  of  X  (a  condition  which  is  indicated  when  the 
galvanometer  pointer  remains  in  the  center  of  the  scale  and  unaffected  when 
the  keys  K  and  KI  are  closed)  if  tjie  key  K2  is  now  closed,  it  will  be  found  that 
when  the  keys  K  and  K\  are  closed  and  opened  at  short  intervals,  the  galvan- 
ometer pointer  will  be  "kicked"  to  one  side  or  the  other  due  to  the  counter 
e.m.f.  of  induction  from  the  magnets  located  in  the  X 
arm  of  the  bridge.  The  counter  current  thus  produced 
is  obviously  of  but  momentary  duration  and  results  in 
the  galvanometer  pointer  being  "kicked"  to  the  right 
or  to  the  left  (depending  upon  the  direction  of  the  flow 
of  current  through  the  galvanometer),  the  pointer  im- 
mediately returning  to  "center."  All  that  is  required 
to  determine  the  inductance  of  the  coil  X  is  to  adjust 
r  and  C  until  there  is  no  "kick"  when  the  keys  K 
and  Ki  are  closed.  Then,  if  the  arms  a  and  b  each  FIG.  78.—  Condenser 
have  100  ohms  resistance  inserted  as  shown  in  Fig.  78,  method  of  measuring 
the  inductance  may  be  determined  by  means  of  the 
formula 

ioo)+RXioo], 


where  h  is  the  inductance  in  henries.1 

1  The  resistance  units  which  make  up  the  values  in  arms  a,  b,  and  R  are  practically 
non-inductive,  as  the  resistance  wire  wound  on  the  "bobbins"  making  up  the  various  units 
is  "doubled  back"  on  itself,  so  that  the  lines  of  force  produced  in  one-half  of  each  coil 
are  "neutralized"  by  those  produced  in  the  other  half,  thus  nullifying  the  inductive  action 
of  the  coil  as  a  whole. 


104  AMERICAN  TELEGRAPH  PRACTICE 

PRACTICAL  ELECTROMAGNET  DATA 

Self-induction  is  proportional  to  the  square  of  the  number  of  turns  of  wire 
in  an  electromagnet,  everything  else  being  equal. 

Connecting  the  windings  of  a  pair  of  magnets  in  "parallel"  reduces  the 
time-constant  one  quarter. 

From  the  formula 

L 

Time-constant  =  ^ 
J\. 

it  is  obvious  that  the  time-constant  of  a  circuit,  including  electro- 
magnets, may  be  reduced  by  reducing  the  self-induction  or  by  increasing  the 
resistance. 

With  the  armature  mounted  so  that  a  distance  of  o.oio  in.  or  more 
separates  it  from  the  pole-faces  of  the  magnets,  maximum  pull  is  obtained 
when  "flat"  pole-faces  are  employed.  When  the  distance  separating 
armature  and  pole-faces  is  less  than  o.oio  in.,  pointed  or  concave  poles  are 
more  effective. 

The  efficiency  of  a  magnet  is  independent  of  the  resistance  of  the  winding. 

It  is  immaterial  whether  a  thick  or  a  thin 
79      conducting  wire  is  used,  provided  the  thickness 
of  the  wire  is  sufficient  to  carry  the  required 

5  1    O    ^|   ^i    *~\  N          a    current,  and  that  the  same  number  of  watts 

-*•—  ^  ~^         are   spent   in  heating  it.     Heat  waste  in  a 

I  —  OOP  —  p\  N  magnet  coil  is  proportional  to  the  square  of 

<_  —J    J    <J    O    J  —  <-         the   current  in  amperes;  magnetizing  power 

^    /-^    ^    s-\  of  the  coil  is  simply  proportional  to  it.     With 

NLj  —  ^_|  —  J  —  <_J  —  (^       7pc    rapidly  varying  currents,  Hughes  found  that 

PIGg  with  a  given  number  of  turns,  the  strongest 

pull  is  obtained  when  the  turns  are  "heaped" 

near  the  poles.  With  constant  currents  the  best  results  are  obtained 
when  the  winding  is  distributed  uniformly  over  the  core. 

There  is  less  magnetic  leakage  between  cores,  and  less  wire  is  required 
per  turn,  when  round  cores  are  used. 

With  small  current  values,  maximum  effect  is  obtained  when  the  poles 
are  situated  1.17  in.  apart. 

With  the  armature  in  contact  with  the  pole-faces  of  the  magnets,  the 
magnetic  leakage  amounts  to  7  per  cent.  With  the  armature  situated  0.004  in  . 
away  the  leakage  amounts  to  53  per  cent. 

The  number  of  turns  of  wire  in  a  single  magnet 


2G2 


ELECTROMAGNETS  105 

Where  L  =  the  length  of  the  winding  space  in  inches, 

D  =  the  diameter  of  the  winding  space  in  inches, 
d  =  diameter  of  the  core  in  inches, 
G  =  the  diameter  of  the  wire,  including  insulation. 

Coil  data  for  the  construction  of  a  i5o-ohm  main-line  relay  of  a  certain 
type  is  as  follows : 

Core:  length,  i  21/32  in.,  diameter  3/8  in. 

Winding  space:  length  i  5/16  in.,  diameter  27/64  in. 

Turns  of  wire:  3,990  turns  of  single  silk-covered  wire  No.  31,  on  each 
spool. 

As  before  stated,  the  direction  of  winding,  and  the  direction  of  current 
through  the  conducting  wire,  determine  which  is  the  south  and  which  the 
north  "pole"  of  the  magnet. 

Figures  79,  790,  79^,  and  79^  show  the  north  and  south  poles,  respectively, 
for  each  combination  of  current  direction,  and  direction  of  winding. 


CHAPTER  VII 
SINGLE  MORSE  CIRCUITS 

The  term  "Single  Morse  line"  is  generally  applied  to  those  circuits  which 
are  so  equipped  and  operated  that  transmission  is  carried  on  in  one  direction 
only  at  a  time. 

The  equipment,  in  the  way  of  apparatus,  of  circuits  so  operated  is  quite 
simple;  in  most  cases,  consisting  of  a  "relay,"  a  "sounder"  and  a  "key"  at 
each  station  or  office  connected  in  the  circuit.  With  the  exception  of  those 
single  circuits  where  an  unusually  large  number  of  offices  are  connected  into 
an  individual  circuit,  the  satisfactory  operation  of  single  Morse  circuits 
does  not  present  any  serious  engineering  problems.  In  general,  the  require- 
ments are  uniformity  of  relay  resistance,  sufficient  current  volume  to  operate 
the  relays,  proper  insulation  of  lines,  and  proper  adjustment  of  armatures 
and  electromagnets  of  both  main-line  and  local  instruments. 


FIG.  80. — Single  Morse  circuit. 

It  may  be  stated  that  these  same  factors  constitute  the  requirements 
of  satisfactory  operation  of  any  system  of  telegraphy  employing  connecting 
wires,  and  while  in  a  measure  this  is  true,  the  fact  remains  that  in  the  opera- 
tion of  other  systems,  such  as  "automatics,"  "printing  systems,"  "multiplex 
systems,"  etc.,  the  factors  above  mentioned  assume  greater  importance, 
and  in  the  operation  of  the  latter  there  are  involved  many  other  factors, 
some  related  to,  and  some  foreign  to  the  essential  elements  above  enumerated. 

The  simple  Morse  circuit  illustrated  in  Fig.  80  operates  upon  the  princi- 
ple that  an  electromagnet  may  be  alternately  magnetized  and  demagnet- 
ized by  closing  and  opening  an  electric  circuit  of  which  the  electromagnet 
forms  a  part. 

Figure  80  represents  a  telegraph  circuit  consisting  of  a  line  -wire  stretch- 
ing between  stations  Y  and  X,  main-line  batteries  B  and  J5i,  electromagnetic 

106 


SINGLE  MORSE  CIRCUITS  107 

relays  R  and  RI,  and  keys  K  and  K\.  To  avoid  the  expense  of  a  return  con- 
ductor between  the  two  stations  in  order  to  "complete"  the  circuit,  the  line 
wire  after  being  connected  through  the  instruments  at  either  end  is 
" grounded,"  that  is,  connected  with  the  ground  by  means  of  an  "earth" 
plate  buried  a  few  feet  below  the  surface  of  the  earth,  or  by  a  metal  rod 
driven  into  the  earth  to  a  depth  of  4  or  5  ft. 

The  completed  circuit  thus  consists  half  of  conducting  wire  and  half  of 
earth.  In  addition  to  the  saving  in  length  of  conducting  wire  required  for 
each  circuit,  this  method  has  the  further  advantage  that  the  electrical  resist- 
ance of  the  circuit  completed  through  the  earth  is  considerably  less  than  if 
completed  by  means  of  a  return  wire,  as  the  resistance  -of  the  earth  is  prac- 
tically negligible. 

Electrical  circuits  made  up  in  this  way  are  called  "ground-return  circuits." 

When  the  circuit  depicted  in  Fig.  80  is  closed  by  means  of  the  key  K, 
(provided  the  key  KI,  also  is  closed)  current  traverses  the  circuit,  energiz- 
ing relays  R  and  RI,  causing  them  to  attract  their  respective  armatures. 
The  effect  upon  the  relays  at  both  stations  is  the  same  whether  the  key  K 
or  KI  is  used  for  the  purpose  of  opening  and  closing  the  circuit.  This  means 
that  manipulating  the  key  at  either  station  results  in  the  simultaneous 
operation  of  all  of  the  relays  connected  in  the  circuit. 

In  the  original  systems  of  telegraphy  the  electromagnetic  instrument 
used  in  place  of  the  modern  "relay"  consisted  of  a  conveniently  mounted 
pair  of  magnets,  the  accompanying  armature  of  which  was  attached  to  one 
end  of  a  lever  having  a  pointed  steel  stylus  at  the  opposite  end  which  indented 
a  mark,  either  long  or  short — depending  upon  the  length  of  time  the  circuit 
was  kept  closed — upon  a  strip  of  paper  tape  continuously  moved  along 
under  it  by  means  of  clock-work,  or  weight-driven  gear.  A  momentary 
contact  produced  a  short  mark,  or  "dot,"  while  a  longer  contact  produced 
a  longer  mark  or  "dash,"  thus  by  alternately  closing  and  opening  the  cir- 
cuit by  means  of  the  sending  key,  in  forming  combinations  of  dots  and  dashes 
to  represent  the  different  letters  of  the  alphabet  (such,  for  instance,  as  "a 
dot  and  a  dash"  for  the  letter  "a,"  "a  dash  and  three  dots"  for  the  letter 
"b"  etc.),  messages  could  be  transmitted  over  the  line  and  ''registered"  on 
the  receiving  tape  in  "dot  and  dash"  signals. 

A  later  development  of  the  receiving  "register"  provided  for  an  inked 
reproduction  of  the  received  signals.  That  is,  the  received  signals  in  the 
form  of  dots  and  dashes  were  marked  on  the  tape  by  means  of  an  inking- 
wheel,  instead  of  being  indented  in  the  paper  as  in  the  original  device. 

It  was  not  long,  however,  until  tape  methods  of  receiving  signals  were 
superseded  by  the  method  at  present  in  use;  that  of  receiving  the  signals  by 
"sound."  In  the  latter  method  the  main-line  relay  in  turn  operates 
locally  a  "sounder"  somewhat  similar  in  construction  to  the  relay  itself  but 
so  designed  mechanically  that  it  gives  forth  a  greater  volume  of  sound,  the 


108  AMERICAN  TELEGRAPH  PRACTICE 

dots  and  dashes  of  the  telegraphic  alphabet  being  recorded  audibly,  and  in- 
stantaneously interpreted  by  ear.  Copying  the  received  message  by  * '  sound" 
requires  that  the  operator  must  be  thoroughly  familiar  with  the  alphabet; 
in  fact,  to  an  extent  that  enables  him  to  recognize  the  Morse  characters 
instantaneously  and  without  having  recourse  to  a  tape  record  of  the  received 
message. 

Referring  again  to  Fig.  80,  it  may  be  observed  that  the  main-line  battery 
at  one  station  is  connected  to  coincide  with  the  battery  at  the  other  station. 
If  the  station  X  has  the  positive  pole  of  his  battery  "to  line"  the  battery  at 
station  Y  is  connected  with  the  negative  pole  to  line.  This  arrangement 
provides  for  a  continuation  of  the  "series"  connection  of  cells,  part  of  the 
battery  being  located  at  one  end  of  the  line  and  part  at  the  other  end. 

In  many  cases  the  battery  for  the  entire  line  is  located  at  one  end  of  the 
circuit.  In  practice  it  is  quite  often  economical  and  convenient  to  maintain 
all  of  the  battery  required  to  operate  the  circuit  or  circuit  at  one  end  only. 

One  disadvantage  of  this  arrangement  is  that  in  case  the  line  becomes 
grounded  any  distance  away  from  the  end  at  which  the  battery  is  located,  the 
stations  beyond  the  "ground"  are  unable  to  communicate  with  each  other 
owing  to  the  fact  that  the  line  beyond  that  point  is  without  battery,  while  in 
those  instances  where  battery  is  maintained  at  each  end  of  the  circuit,  offices 
on  each  side  of  the  temporary  ground  connection  may  keep  up  communica- 
tion with  each  other  locally  during  the  enforced  interruption  to  the  through 
circuit. 

On  single  circuits  such  as  those  under  consideration,  an  indefinite  number 
of  intermediate  offices  may  be  introduced  in  the  circuit  between  the  two 
terminal  offices,  each  intermediate  office  being  equipped  with  its  relay,  key, 
and  sounder.  The  manipulation  of  any  key  connected  into  the  circuit  oper- 
ates all  of  the  relays  simultaneously.  When  any  key  is  being  used  to  trans- 
mit signals  it  is  necessary,  of  course,  that  all  other  keys  be  kept  closed,  except 
for  the  purpose  of  "breaking"  and  calling  for  the  repetition  of  doubtful 
words  on  the  part  of  the  operator  receiving  the  message.  This  is  what  is 
known  as  the  "closed-circuit"  system. 

THE  LOCAL  CIRCUIT 

Main  telegraph  lines  stretching  between  towns  and  cities  have  a  com- 
paratively high  resistance,  and,  generally  speaking,  it  is  more  convenient  and 
economical  to  employ  a  main-line  receiving  instrument  designed  to  operate 
on  a  small  volume  of  current,  say,  from  40  to  75  milliamperes,  rather  than  an 
instrument  which  requires  large  current  volumes. 

With  a  current  of  less  than  one-tenth  of  an  ampere  a  sufficient  magnetic 
force  is  not  developed  in  the  electromagnets  of  a  receiving  instrument  to 
attract  the  armature  with  the  power  necessary  to  produce  an  adequate  vol- 


SINGLE  MORSE  CIRCUITS  109 

ume  of  sound  when  the  armature  strikes  the  "stop"  screws  in  the  act  of 
reproducing  the  received  signals. 

In  order  to  obtain  a  satisfactory  volume  of  sound  it  is  necessary  to  employ 
armatures  having  considerable  size  and  weight,  and  the  satisfactory  operation 
of  such  comparatively  large  moving  parts  requires  strong  magnetic  action 
on  the  part  of  the  electromagnets  actuating  the  armature. 

Instead  of  employing  large  currents  to  overcome  the  resistance  of  the 
entire  line  conductor  in  order  to  obtain  strong  magnetic  action  in  the 
receiving  instrument,  it  is  much  more  economical  to  use  a  sensitive  receiving 
instrument  operated  on  low-current  values,  and  to  provide  that  the  armature 
of  the  more  delicate  line  instrument  shall  automatically  close  and  open  a 
" local"  circuit  in  response  to  the  closing  and  opening  of  the  main-line  circuit. 

It  is  an  easy  matter  to  arrange    for  current  values  in  the  local  circuit 


Line 


FIG.  81. — The  sounder  circuit. 

to  suit  the  requirements,  as  there  is  no  resistance  to  be  overcome  except 
that  of  the  magnet  windings  of  the  local  instrument  used  as  a  "sounder" 
and  the  comparatively  short  lengths  of  conducting  wire  necessary  to  make 
the  desired  connections. 

Figure  81  shows  theoretically  the  connections  of  one  end  of  a  single 
Morse  circuit,  with  relay  R,  key  K,  and  main  battery  MB,  connected  in 
series  in  the  main-line  circuit,  while  the  local  circuit  with  local  battery  LB, 
and  sounder  S,  are  connected  in  series  through  the  armature  A ,  and  closed 
contact  C,  of  the  relay.  The  operation  of  the  local  or  "reading"  circuit 
may  be  readily  traced.  When  the  main  circuit  or  line  is  closed,  the  relay 
magnet  attracts  its  armature  and  closes  -the  local  circuit,  in  which  is  located 
the  magnet  of  sounder  5.  The  relay  armature  is  of  such  light  construction 
that  a  weak  current  is  sufficient  to  operate  it,  while  the  resistance  of  the 
local  circuit  is  so  low  that  practically  the  entire  force  of  the  local  battery  is 
available  to  operate  the  sounder. 

It  may  be  noted  that  although  the  local  circuit  depends  for  its  operation 
upon  the  operation  of  the  main  circuit,  the  latter  is  separate  and  independ- 
ent of  the  former  and  is  in  no  way  affected  by  its  action. 


110 


AMERICAN  TELEGRAPH  PRACTICE 


OPEN-CIRCUIT  SYSTEM 

A  main-line  circuit  may  be  arranged  between  two  stations  as  shown  in 
Fig.  82  (a  system  much  used  in  Europe),  in  which  a  main-line  battery  situated 
at  either  end  of  the  line  is  brought  into  action  only  when  the  line  is  in  use  for 
the  actual  transmission  of  signals.  In  the  diagram,  two  terminal  stations 
and  an  intermediate  station  are  shown,  each  having  a  battery,  relay,  and  key. 
The  main-line  connection  is  made  to  the  "lever"  of  the  key,  thus  the  circuit 
divides  at  that  point  into  two  branches,  but  one  of  which  can  be  closed  at 
one  time.  One  of  the  branches  includes  the  battery  and  the  ground  connec- 
tion only,  while  the  other  takes  in  the  magnet  windings  of  the  relay  and  con- 
tinues to  the  ground  connection.  Normally  the  key  at  each  station  rests 
in  a  position  which  closes  the  line  circuit  through  the  receiving  relay  to 
ground. 


K                                               1    K 

~l 

TJL 

- 

^-B 

-^ 

- 

—  *—  ' 

7" 

FIG.  82. — "Open  circuit"  Morse  system. 

The  transmission  of  signals  is  accomplished  by  depressing  the  key, 
which  establishes  connection  between  the  battery  and  the  line,  and  as  the 
receiving  relay  at  the  distant  station  is  normally  in  the  main-line  circuit, 
the  signals  transmitted  from  the  sending  station  are  received  in  the  same 
manner  as  in  the  closed-circuit  system  (for  the  sake  of  simplicity  the  local 
circuits  at  each  station  have  been  left  out  of  the  diagram,  Fig.  82). 

While,  in  this  country  there  are  not  many  telegraph  circuits  which  are 
not  in  use  the  major  portion  of  the  day,  the  open-circuit  system,  permitting 
as  it  does  of  the  use  of  dry  cells,  affords  a  simple  and  comparatively  eco- 
nomical means  of  operating  short  wires,  private  lines,  and  lines  between  points 
remote  from  regulation  sources  of  electric  current,  where  the  transportation, 
setting  up  and  maintenance  of  chemical  batteries  might  involve  objection- 
able features.  The  connections  as  shown  in  Fig.  82  are  such  that  the  relay 
at  the  sending  station  does  not  record  the  outgoing  signals,  the  object  being 
to  eliminate  the  resistance  of  the  relay  at  the  sending  station  during  the 
transmission  of  a  message  so  that  a  greater  volume  of  current  will  be  available 
to  actuate  the  other  relays  in  the  circuit.  Where  this  system  is  used,  in 


SINGLE  MORSE  CIRCUITS 


111 


some  instances  a  low-resistance  galvanometer  is  provided  and  inserted  on 
the  "line"  side  of  the  key  at  each  office  for  the  purpose  of  giving  the  sending 
operator  an  indication  of  the  outgoing  signals.  It  is  obvious,  however, 
that  where  a  sufficient  number  of  cells  of  battery  are  used,  the  relay  connected 
into  the  circuit  at  each  office  could  be  inserted  as  shown  in  Fig.  83  instead 
of  as  shown  in  Fig.  82,  in  which  case  the  outgoing  signals  would  be  recorded 
on  the  home  relay  in  the  same  way  as  in  the  closed-circuit  system  of 
operation. 


FIG.  83. 


SEVERAL  LINES  WORKED  OUT  OF  A  SINGLE  BATTERY 

It  is  a  singular  fact  that  a  source  of  e.m.f.  having  a  sufficient  output  to 
operate  one  line  will  work  several  lines  with  equal  facility,  provided  there 
is  not  too  great  a  difference  in  the  lengths  or  resistances  of  the  individual 
conductors.  In  practice,  variations  in  length  of  the  several  conductors 
connected  to  a  single-battery  or  dynamo-electric  machine  may  be  com- 
pensated (in  the  case  of  a  very  short  line,  or  one  having  low  resistance  in 
comparison  with  the  other  lines  being  fed  by  the  battery)  by  inserting  an 
additional  resistance  in  the  form  of  a  coil  of  wire  in  series  with  the  low- 
resistance  line,  so  that  its  total  resistance  will  be  raised  to  a  value  which 
will  prevent  the  short  wire  acting  as  a  low  resistance  path  to  ground  for  the 
battery  current. 

A  No.  8  B.  W.  G.  iron  wire  weighing  380  Ib.  per  mile  has  a  resistance  of 
12.37  onms  per  mile  at  a  temperature  of  68°  F.,  and  a  No.  9  B.  &  S.  gage 
copper  wire  weighing  208  Ib.  per  mile  has  a  Distance  of  4.39  ohms  per  mile 
at  the  same  temperature. 

Assume  that  we  have  a  ground  return  circuit  connecting  two  terminal 
stations  100  miles  apart,  and  that  there  are  two  intermediate  offices  con- 
nected in  the  circuit,  and  that  each  station  is  equipped  with  a  receiving 
instrument  having  a  resistance  of  150  ohms.  If  the  source  of  current  to 
operate  the  line  consists  of  a  gravity  battery,  and  a  current  of  50  milliamperes 
is  required  to  satisfactorily  operate  the  circuit,  first  ascertain  the  resistance 
of  the  line,  including  the  resistance  of  the  windings  of  the  magnets  of  all  of 


112  AMERICAN  TELEGRAPH  PRACTICE 

the  receiving  instruments  in  circuit.     Then,  assuming  that  the  line  con- 
ductor consists  of  No.  8  iron  wire,  we  have 

100  miles  of  No.  8  iron  wire  at  12.37  ohms  per  mile=  1,237  ohms, 
4  receiving  instruments  each  having  150  ohms  re- 
sistance =      600  ohms 


Total,  i>837  ohms. 

The  number  of  cells  of  gravity  battery  required  to  furnish  50  milliamperes 
of  current  through  a  resistance  of  1,837  ohms  may  be  ascertained  by  means 
of  the  formula  given  on  page  75.  In  this  instance  the  values  of  the  various 
factors  are 

^  =  1,837  ohms, 
£  =  1.07  volts 
^  =  2.5  ohms, 
7  =  0.050  ampere 

n 

and  as  the  number  of  cells  (N)    =^  — 

£L 

rr 

then  ^1  --  i       cells. 


0.050 

The  reason  that  the  law 


does  not  correctly  apply  for  this  purpose  is  that  each  cell  of  battery  has  a 
resistance  of  2  1/2  ohms,  and  the  97  cells  place  an  additional  243  1/2  ohms 
resistance  in  the  circuit.  However,  after  the  value  of  E  for  the  entire 
battery  has  been  determined  by  the  above  method,  the  simpler  formula 

Tf 

I=X  may  be  employed  to  check  the  result.     The  example  here  considered, 

where  the  resistance  per  mile  of  the  conductor  has  been  multiplied  by  the 
number  of  miles,  assumes  perfect  insulation  of  the  line. 

The  97  cells  of  battery  required  to  furnish  50  milliamperes  current  would 
not  necessarily  have  to  be  located  at  one  end  of  the  line,  but  might  be  dis- 
tributed, part  at  one  end  and  part  at  the  other,  in  which  latter  case  opposite 
battery  "  poles"  should  be  placed  to  line  at  each  terminal  station  —  positive 
at  one  end  and  negative  at  the  other. 

If  the  source  of  e.m.f.  availed  of  to  furnish  current  to  operate  the  line 

Tf 

above  considered  were  a  dynamo,  then  the  formula  I=n  would  serve  the 
purpose,  as  the  internal  resistance  of  the  dynamo  is  so  low  as  to  be  negligible. 


SINGLE  MORSE  CIRCUITS 


113 


Suppose  two  terminal  stations  situated  500  miles  apart  are  connected  by 
a  No.  9  copper  wire,  and  that  there  are  two  intermediate  stations  in  the 
circuit,  each  station,  including  the  two  terminals,  being  equipped  with  re- 
ceiving instruments  having  150  ohms  resistance  (Fig.  84).  If  we  assume 
the  line  to  be  perfectly  insulated  and  it  is  desired  to  ascertain  the  voltage 
necessary  to  maintain  45  miliamperes  current  in  the  circuit  by  means  of  the 
formula  E  =  IXR}  the  required  potential  may  be  arrived  at  thus: 


FIG.  84. 


=  0.045  ampere 


2,795  ohms, 
and 

2,795X0.045  =125.775,  or  126  volts. 

In  this  example  we  have  not  allowed  for  the  insertion  of  any  additional 
resistance  in  applying  the  e.m.f.  to  the  circuit.  This  imposes  the  require- 
ment that  the  source  of  e.m.f.  must  have  very  little  or  no  internal  resist- 
ance if  45  milliamperes  current  is  to  be  maintained  in  the  external  circuit. 

As  previously  stated,  several  lines  may  be  worked  out  of  one  battery, 
and  in  practice  it  is  found  that  when  the  internal  resistance  of  the  source  of 


i 

=T. 

2 

=•              -3 

•  T                                      3 

ij 

FIG.  85. — Several  lines  fed  from  a  common  battery. 

e.m.f.  is  infinitely  small  in  comparison  with  that  of  the  several  lines  connected 
thereto,  the  strength  of  the  current  in  each  circuit  will  be  practically  the  same 
as  if  it  were  the  only  line  attached  to  the  battery.  In  view  of  this  when  a 
number  of  lines  are  "fed"  from  a  common  battery  it  is  immaterial  whether 
but  a  single  line  is  operated,  or  whether  several  lines  are  operated 
simultaneously. 

By  reviewing  the  calculations  in  connection  with  Figs.  64  and  640  on  page 
85,  dealing  with  joint-resistance,  the  student  will  be  better  able  to  under- 
stand the  explanation  of  this  seeming  inconsistency  in  the  behavior  of 
electric  currents. 

8 


114  AMERICAN  TELEGRAPH  PRACTICE 

When  a  single  line  is  being  fed  from  a  battery,  and  a  second  and  a  third 
line  are  connected  to  the  same  source  as  in  Fig.  85,  the  total  amount  of 
current  flowing  from  the  battery  divides  along  three  paths  and  when  all 
three  circuits  are  closed,  that  is  to  say;  taking  current,  the  aggregate  sec- 
tional area  of  the  conductor  is  so  increased  that  the  total  resistance  which 
limits  the  volume  of  current  flowing  from  the  battery  is  greatly  reduced, 
and  as  the  strength  of  current  taken  from  the  battery  increases  in  the  same 
proportion,  the  loss  which  would  result  from  the  division  of  the  current  into 
three  separate  branches  is  compensated  for  by  the  increased  current  strength 
due  to  the  reduction  in  resistance  of  the  circuit  as  a  whole. 

The  maximum  current  efficiency  may  be  derived  from  a  battery  when  the 
total  internal  resistance  of  the  battery  equals  the  resistance  of  the  external 
circuit.  Of  course,  actual  conditions  are  such  that  it  is  not  convenient,  or 
for  that  matter  necessary  to  maintain  this  balance  of  resistance  between  the 
external  and  internal  portions  of  the  circuit,  but  it  is  due  to  this  that  the 
gravity  cell,  with  its  comparatively  high  internal  resistance  per  cell  (2  1/2 
ohms),  has  met  the  requirements  so  satisfactorily,  and  that  this  type  of 
battery  has  been  so  extensively  employed  in  the  operation  of  telegraph  lines. 
The  longer  the  line,  or  rather  the  greater  the  resistance  of  the  line,  the  better 
does  this  type  of  cell  answer  the  purpose,  but  this  is  true  only  when  each 
separate  line  has  its  own  battery. 

When  the  battery  is  required  to  feed  several  lines,  the  internal  resistance 
becomes  an  important  factor.  By  considering  the  conditions  which  prevail 
in  a  case  such  as  that  depicted  in  Fig.  85  it  is  evident  that  the  internal 
resistance  of  the  battery  will  remain  constant  while  the  resistance  of  the 
circuit  beyond  the  point  X  will  vary  considerably,  depending  upon  the 
number  of  branches  which  are  closed  at  one  time.  As  the  battery  resistance 
then  becomes  an  important  part  of  the  total  resistance  of  the  circuit,  the 
former  should  be  kept  as  low  as  is  practicable,  for,  no  matter  whether  one  or 
more  lines  are  being  operated  at  the  same  time,  each  line  should  have  equal 
current  strength. 

When  a  battery  composed  of  gravity  cells  is  employed  to  feed  several 
lines,  the  current  volume  in  each  separate  circuit  varies  according  to  the 
number  of  circuits  which  are  closed  at  the  same  time. 

Suppose,  for  instance,  that  five  separate  lines  each  having  a  total  resistance 
of  1,200  ohms  are  fed  from  a  gravity  battery  having  a  total  e.m.f.  of  100 
volts  and  a  total  internal  resistance  of  200  ohms,  then  with  one  circuit 
"closed"  and  the  other  four 'open,  the  current  value  in  the  closed  conductor 
would  be 

E 


1  = 


r+R 

100 

—  =  71  m.a. 
200+1,200 


SINGLE  MORSE  CIRCUITS  115 

With  all  five  circuits  closed,  the  current  value  obtaining  in  each  circuit 
may  be  determined  by  means  of  the  formula 

T      E 

1  =  -  —  $-# 


TOO 

=  —  -  -5-5  =  45  m.  a. 

,  1,200     ° 
200  H  —  - 

Or,  as  the  five  circuits  are  operated  simultaneously  or  intermittently  the 
volume  of  current  in  each  conductor  will  fluctuate  between  45  milliamperes 
and  71  milliamperes,  depending  upon  the  number  of  circuits  which  are  closed 
at  one  time.  In  this  particular  instance  the  discrepancy  between  maximum 
and  minimum  current  values  in  any  one  circuit  may  not  be  great  enough  to  be' 
regarded  as  unsatisfactory,  but  it  should  be  noted  that  the  conditions  are 
such  that  the  minimum  current  value  is  still  high  enough  to  operate  the 
usual  type  of  receiving  instrument  under  favorable  conditions,  also  the 
resistance  of  each  of  the  five  lines  is  identical,  and  further;  but  five  lines  are 
being  fed  from  the  battery.  Obviously,  if  the  number  of  lines  were  increased, 
or  if  the  individual  resistances  of  the  various  lines  should  be  unequal,  the 
unsuitability  of  primary  batteries  for  the  purpose  of  supplying  current  to 
many  lines  would  be  more  apparent.  If,  for  instance,  the  number  of  lines 
in  the  above  example  should  be  increased  to  six,  then  (other  conditions 
remaining  the  same)  the  minimum  current  would  be  25  milliamperes,  a 
value  too  low  for  single-circuit  operation. 

Where  secondary-cells  or  dynamo  machines  are  employed  to  furnish 
current  to  operate  telegraph  lines,  the  negligible  internal  resitsance  of  these 
sources  of  e.m.f.  fulfills  the  condition  previously  referred  to  "where  the 
internal  resistance  of  the  source  of  e.m.f.  is  infinitely  small  in  comparison 
with  that  of  the  several  lines  connected  thereto,"  and  if  the  five  lines  con- 
sidered in  the  above  example  were  supplied  with  current  from  a  dynamo 
having  an  e.m.f.  of  100  volts,  the  current  strength  in  the  closed  conductor 
(the  other  four  remaining  open)  would  equal 

100 

=  83  m.a. 


1,200 

and  with  all  five  circuits  closed, 

100 


1200 


^-5  =  83  m.a. 


5 

If  instead  of  five  circuits,  ten  are  connected  to  the  same  source  of  e.m.f. 
the  current  value  in  one  closed  circuit  would  be 

I0°  O 

83  m.a. 

° 


1200 


116  AMERICAN  TELEGRAPH  PRACTICE 

and  with  all  ten  circuits  closed  simultaneously,  the  current  volume  in  each 
circuit  would  be 

=  8    m. a. 


1200 
10 

Thus,  when  several  lines  are  fed  from  a  dynamo,  the  current  values  obtaining 
in  each  circuit  are  constant,  and  independent  of  the  closing  or  opening  of  other 
circuits  fed  from  the  same  source. 

The  foregoing  examples  assume  identical  resistance  values  for  the  various 
circuits  fed  from  a  common  source  of  e.m.f.  In  those  applications  where 
the  individual  resistances  of  the  various  circuits  fed  from  a  common  battery 
are  not  "evened  up,"  it  must  be  remembered  that  the  current  in  a  circuit 
varies  directly  as  the  electromotive  force,  and  inversely  as  the  resistance  of 
the  circuit. 

Suppose,  for  example,  that  a  loo-volt  dynamo  is  employed  to  feed  three 
circuits,  the  first  having  1,000  ohms,  the  second  2,000  ohms,  and  the  third 
3,000  ohms  resistance.  By  means  of  the  formula  given  on  page  84  for 
calculating  joint-resistance,  the  joint-resistance  of  these  three  circuits  would 
be  545  ohms.  The  total  current  strength  in  the  joint  circuit  would  equal 

100 
—  =  183  m.a. 

545 

and  the  portion  of  the  total  current  traversing  each  branch  may  be  ascertained 
thus: 

T         T>         T  I0° 

In  AI,  I  —  —    —  =  loom. a. 

1000 

T         T>          T  I0° 

In  7?2,  /  =  —    —  =   50  m.a. 

2OOO 

,     ~  100 

183  m.a. 

MORSE  SINGLE-LINE  INSTRUMENTS 

Figure  86  gives  a  view  of  a  Morse  key  equipped  with  extension  "legs"  to 
be  used  in  fastening  the  key  on  top  of  the  operating  table.  This  type  of 
sending  key,  which  is  known  as  the  "Bunnell  steel  lever  key,"  is  at  the 
present  time  quite  generally  employed  in  commercial  and  railroad  telegraphy. 
Its  construction  combines  lightness  of  moving  parts,  durability,  and  ease  of 
adjustment. 

Figure  87  illustrates  another  form  of  the  same  type  of  key,  designed  to 
be  fastened  to  the  operating  table  by  means  of  ordinary  screw  nails.  In- 


SINGLE  MORSE  CIRCUITS 


117 


FIG.  86. — Bunnell  key,  "leg"  type. 


FIG.  87. 


Local  Circuit 


Main  Line 


1 


Main 
Battery 


FIG.  88. — Morse  relay,  skeleton  connections. 


118 


AMERICAN  TELEGRAPH  PRACTICE 


stead  of  the  connecting  wires  being  attached  to  "legs"  as  in  the  form  of  key 
illustrated  in  Fig.  86,  two  binding-posts  mounted  on  the  base  of  the  key 
serve  to  hold  the  wires  which  connect  the  key  into  the  circuit. 

Figure  88  shows  the  binding-post  and  internal  connections,  both  main 
line  and  local,  of  a  main-line  "relay"  of  the  usual  type.     For  the  sake  of 


FIG.  89. — Morse  relay. 


k 


FIG.  90. — Morse  sounder. 


clearness,  a  few  turns  only  of  magnet  wire  are  shown  wound  around  the  core 
of  each  spool.  The  way  in  which  the  movable  armature  tongue  when 
attracted  by  the  magnets  connected  in  the  main-line  circuit  closes  the  local 
circuit,  thus  operating  the  reading  sounder,  may  easily  be  traced  in  the  drawing. 
Figure  89  shows  a  relay  completely  assembled,  and  Fig.  90  a  view  of  a 
type  of  sounder  extensively  employed  in  this  country. 


CHAPTER  VIII 

LIGHTNING  AND  LIGHTNING  ARRESTERS— FUSES— GROUND 

CONNECTIONS 

For  many  years  it  was  believed  that  lightning  was  simply  an  alternating 
current  of  very  high  frequency.  During  the  past  20  years,  however,  a  large 
amount  of  research  work  has  been  carried  on  with  the  object  of  learning 
something  definite  and  conclusive  in  regard  to  the  nature  of  lightning  dis- 
charges, and  it  is  now  known  that  lightning  may  be  manifested  in  several 
different  ways. 

A  lightning  disturbance  may  occur  as: 

A  single  discharge  of  very  high  potential. 

As  an  alternating   current  of  comparatively  low  frequency,  having 

greater  inductive  than  static  effects. 

As  an  alternating  current  of  high  frequency,  having  large  capacity 
and  high  self-induction. 

When  lightning  strikes  a  telegraph  line,  a  part  of  the  line  may  be  de- 
stroyed due  to  the  charge  reaching  the  ground  by  way  of  the  poles,  the  latter 
being  split  and  torn  as  if  from  internal  explosion. 

When  lines  are  provided  with  ground  wires  attached  to  poles  and  fixed 
close  to  the  conducting  wires,  and  with  lightning  arresters  at  terminals,  the 
charge  is  divided,  reaching  the  earth  at  as  many  points  as  are  presented  in 
the  form  of  discharge-gaps.  But  even  if  the  charge  has.  been  quickly 
drained  off,  its  presence  upon  the  conductor  even  for  a  brief  interval  of 
time  affects  the  electric  circuit  so  that  a  disturbance  more  or  less  pro- 
nounced is  the  result. 

The  single  discharge  of  high  potential,  or  the  direct  stroke  as  it  is  some- 
times called,  although  rare  in  comparison  with  the  number  of  disturbances 
due  to  electrostatic  induction,  is  more  disastrous  to  property.  The  imme- 
diate, or  local  effects  of  the  direct  flash  include  the  shattering  of  glass  or 
other  insulators,  splintering  of  crossarms  and  poles;  incidental  to  the  passage 
of  the  discharge  to  ground,  as  referred  to  above.  The  damage  may  be  con- 
fined to  a  short  section  of  the  line,  sometimes  two  or  three  pole  lengths,  or 
may  extend  over  a  distance  of  a  mile.  In  most  cases  the  severity  of  the 
damage  decreases  with  the  distance  from  the  point  at  which  the  discharge 
takes  place.  The  fact  that  beyond  a  comparatively  short  distance  from  the 
center  of  shock  there  is  no  visible  damage  to  the  line  does  not  mean  that  the 
discharge  has  been  completely  dissipated,  but  rather  that  the  current  induced 

119 


120  AMERICAN  TELEGRAPH  PRACTICE 

in  the  conducting  wire  has  after  traveling  an  indefinite  distance  along  the 
conductor  become  attenuated  to  an  extent  that  robs  the  charge  of  its  power 
to  do  further  damage  of  the  nature  cited  above.  In  the  conductor,  however, 
there  has  been  started  a  current  wave  progressing  outward  which  causes  a 
surging  likely  to  produce  indirect  disturbances  at  distant  points  in  the  circuit. 

Analogous  to  the  way  in  which  a  river  may  rise  until  dams  and  embank- 
ments give  way,  an  induced  charge  of  electricity  mav  accumulate  in  a  circuit 
as  a  result  of  rain,  snow,  fog,  or  clouds  of  dust  being  driven  across  the  line, 
until  the  difference  of  potential  between  line  and  ground  assumes  enormous 
proportions,  and  at  the  breaking-point  discharges  across  lightning  arresters 
attached  to  the  line,  and,  seeking  paths  of  least  resistance,  discharges  to  ground 
through  the  intervening  dielectric. 

If  a  positively  charged  cloud  passes  over  a  line,  an  electrostatic  charge 
may  be  induced  in  which  the  earth  below  the  line  assumes  a  negative  electro- 
static charge.  The  line  itself,  due  to  its  more  elevated  position,  also  takes 
on  a  negative  charge,  somewhat  higher  in  potential  than  that  of  the  earth, 
Of  course,  the  sign  of  the  charge  on  the  conductor  depends  greatly  upon  the 
degree  of  insulation  maintained  between  the  line  and  the  ground.  As  a 
positively  charged  cloud  approaches  a  perfectly  insulated  line  the  latter 
may  assume  a  positive  charge  at  cloud  potential,  and  as  the  potential  rises 
with  the  approach  of  the  cloud,  the  potential  difference  between  line  and 
earth  may  rise  to  a  point  where  discharge  takes  place  between  the  earth  and 
the  line.  As  the  cloud  recedes  from  the  line,  the  latter  then  remains  nega- 
tively charged  and,  inasmuch  as  this  charge  is  no  longer  bound  by  the  posi- 
tive charge  of  the  cloud,  a  discharge  takes  place  from  line  to  earth. .  When 
an  electrostatic  charge  affects  a  line,  there  is  a  strain  of  contending  forces — 
potentials  at  opposite  polarities;  naturally  disruption  takes  place  when  these 
forces  meet.  The  enormous  strain  manifested  is  not  confined  to  the  conduct- 
ing wire  or  wires,  but  embraces  all  neighboring  conductors  or  semiconductors, 
so  much  so  that  in  certain  instances  persons  standing  25  or  more  feet  away 
from  where  the  chief  damage  has  been  wrought  have  been  severely  shocked. 

Undoubtedly  the  most  frequent  manifestations  of  atmospheric  electricity 
in  line  conductors  are  the  result  of  electrostatic  induction  from  passing 
clouds.  Each  readjustment  between  cloud  and  ground  or  between  cloud 
and  cloud  in  the  neighborhood  of  a  conducting  circuit  brings  about  an  abrupt 
alteration  in  the  electrostatic  charge  on  that  part  of  the  line  immediately 
in  the  vicinity  of  the  disturbance.  The  induced  impulses  in  the  circuit 
increase  in  strength  and  frequency  as  the  cloud  approaches  the  line  and 
decrease  as  the  cloud  recedes. 

The  popular  scientific  conception  of  the  conditions  which  exist,  in  the 
atmosphere  when  an  oscillatory  discharge  takes  place  assumes  that  the  air, 
the  cloud  and  the  earth,  in  effect,  constitute  a  huge  condenser  with  the  air 
as  the  dielectric.  It  is  true,  of  course,  that  the  dielectric  in  this  case  is  con- 


LIGHTNING  AND  LIGHTNING  ARRESTERS 


121 


FIG.  91. — "Saw-tooth"  lightning  arrester. 


stantly  varying  in  density,  purity,  and  humidity,  and  this  inconstancy  of  the 
insulating  medium;  in  a  measure  accounts  for  the  variegated  effects  observed. 
When  the  air  breaks  down  under  the  strain  and  becomes  heated  to  incandes- 
cence, the  phenomenon  observed  is  called  lightning. 

Many  years  ago  it  was  discovered  that  a  lightning  discharge  traveling 
through  a  conducting  wire  has,  so  to  speak,  an  aversion  to  turning  corners, 
insisting  to  its  utmost  upon  traveling  in  a  straight  path.  The  excessive 
heating  effects  of  these  induced  charges  often  deflagrate  telegraph  wires 
at  points  where  the  conductor  has  been  injured  mechanically  (thus  reducing 
its  cross-section)  or  where  the 
wire  is  "kinked"  or  bent.  In 
the  design  of  modern  lightning 
arresters  advantage  has  been 
taken  of  the  fact  that  " kinks" 
or  turns  of  wire  serve  to 
" choke"  the  induced  oscilla- 
tory currents.  Thus  in  several 
forms  of  arresters  employed  to 
protect  aerial  lines  a  choke-coil 
forms  an  important  element  of 
the  arrester. 

The  design  of  satisfactory 

protectors  should  provide  against  undue  prolongation  of  abnormal  currents 
in  the  conductor.  This  is  accomplished  by  means  of  a  properly  designed 
"fuse."  Also  an  air-gap  or  high-resistance  path  to  earth  should  be  pro- 
vided for  high-potential  discharges.  This  may  consist  of  two  metal  plates, 
one  connected  with  the  earth  and  the  other  with  the  line  wire,  one  plate 
being  provided  with  pointed  "saw-teeth"  as  illustrated  in  Fig.  91.  This 
lightning  arrester  is  seldom  seen  except  in  the  older  installations. 

Where  it  is  required  to  guard  against  high  potentials,  it  is  customary  to 
employ  an  arrester  which  offers,  for  large  currents,  a  path  to  earth  having  a 
lower  break-down  point  than  is  offered  by  the  insulation  of  the  circuit  pro- 
tected. Most  protectors  designed  with  this  end  in  view  consist  of  two  con- 
ducting surfaces,  one  of  which  is  connected  to  the  line  conductor  and  the 
other  to  the  earth.  The  two  sides  of  the  arrester  may  be  separated  by  a 
gap,  either  in  open  air  or  in  a  vacuum,  or  they  may  be  separated  by  a  high- 
resistance  material  such,  for  instance,  as  carborundum.  The  sensitiveness 
of  a  lightning  arrester  depends  considerably  upon  the  width  of  space  separating 
the  metallic  or  conducting  elements  of  the  arrester,  and,  although  in  practice 
arresters  are  employed  having  spacings  of  0.005  to  o.oio,  and  as  high  as  o.ioo 
in.,  depending  upon  locality  and  character  of  protection,  it  is  important  that 
accurate  spacing  be  maintained. 

Figure  92  shows  one  form  of  arrester  consisting  of  spring  clips  5  and 


122  AMERICAN  TELEGRAPH  PRACTICE 


FIG.  92. — Carbon-block  arrester. 
,Line 


•fr 


Apparatus 


FIG.  93. — Vacuum-gap  arrester. 


FIG.  94. 


LIGHTNING  AND  LIGHTNING  ARRESTERS 


123 


-?-  -  -m 


Sij  carbon  blocks  C  and  Ci,  and  separator  M,  the  latter  being  made  up  of 
strips  of  mica  to  the  desired  thickness.  The  mica  separator  is  perforated  in 
several  places,  thus  making  as  many  air-gaps  between  the  two  carbon  blocks, 
the  latter  being  in  contact  with  the  spring  clips  which  in  turn  are  connected 
to  line  and  ground  respectively. 

In  this  form  of  arrester  it  is  of  the  greatest  importance  that  a  high  grade 
of  carbon  be  used  in  making  the  blocks,  as  the  poorer  grades  are  liable  to 
"chip"  or  to  oxidize  and  form  carbon  dust,  and  thus  interfere  with  the 
correct  spacing  of  the  blocks. 

Other  forms  of  this  type  of  arrester  which 
have  recently  been  introduced  are  the  "vacuum 
gap"  and  the  "Brach." 

The  former  is  shown  diagrammatically  in  P'ig. 
93.  In  this  make  of  air-gap  arrester  the  dis- 
charge takes  place  in  the  form  of  a  "brush" 
between  two  carbon  plates  separated  by  a  par- 
tial vacuum.  It  is  well  known  that  an  electrical  m 
discharge  will  take  place  between  two  conduct- 
ing surfaces  at  a  lower  potential  in  a  vacuum 
than  in  air  at  ordinary  pressures.  Thus,  a 
greater  separation  of  plates  may  be  maintained 
when  the  discharge  takes  place  in  a  vacuum. 

The  opposing  surfaces  of  the  carbon  blocks — 
as  in  the  original  metal-plate  arrester — are  ser- 
rated, and  there  is  no  carbon  dust  produced 
which  would  form  a  deposit  likely  to  reduce  the 
insulation  existing  between  the  terminals  of  the  JTIG-  95.— Combination  saw- 
arrester,  tooth  and  carborundum-block 

Figure  94  gives  a  photographic  view  of  the  arrester, 
vacuum  arrester. 

In  the  Brach  arrester  a  direct  contact  path  from  line  to  earth  is  provided 
through  a  high-resistance  block  which  separates  the  metallic  surfaces  of  the 
arrester.  See  Fig.  95. 

The  cut  shows  an  arrester  equipped  with  fuses  and  an  auxiliary  air-gap 
of  the  older  form.  The  departure  from  the  air-gap  principle  embodied  in 
this  arrester  is  illustrated  at  the  lower  extremity  of  the  arrester  elements 
and  between  the  fuses,  where  M  represents  metallic  plates,  C,  carbon  plates, 
and  R,  blocks  of  a  high-resistance  compound.  The  cut  shows  a  two-line  unit. 

The  separator  blocks  used  in  this  arrester  have  a  resistance  of  about  4 
megohms  when  subjected  to  a  pressure  of  240  volts,  the  resistance  decreasing 
rapidly  as  the  potential  is  increased. 

Where  arresters  of  the  direct-contact  type  are  distributed  at  intervals 
along  a  line,  it  is  evident  that  the  total  insulation  of  the  line  will  be  somewhat 


124  AMERICAN  TELEGRAPH  PRACTICE 

reduced,  but  where  a  high  degree  of  insulation  between  line  and  earth  is  not 
essential,  the  "static"  draining  possibilities  of  this  type  of  arrester  may  be  of 
considerable  advantage. 

As  a  protection  against  oscillatory  currents  of  high  frequency  and  large 
self-induction,  a  "choke"  coil  may  be  included  as  an  element  of  the  arrester. 
A  length  of  2  or  3  ft.  of  insulated  wire  wound  into  a  coil  J  or  J  in.  in  diameter, 
when  inserted  in  the  line  constitutes  an  effective  barrier  to  the  passage  of 
high-frequency  alternating  currents.  A  well-known  form  of  arrester  which 
embodies  the  principles  above  referred  to  is  that  known  as  the  Argus. 

A  well-designed  form  of  choke  coil  as  employed  in  guarding  against 
lightning  discharges  is  shown  in  Fig.  96,  in  which  the  conductor  is  carried 
through  a  spirally  turned  pipe  of  small  diameter.  The  section  of  the 


FIG.  96. — Lightning  choke-coil. 

conducting  wire  enclosed  in  the  iron-pipe  spiral  is  insulated,  thus  are  combined 
two  forms  of  impedance.  The  discharge-rod  shown  traversing  the  entire  coil 
acts  to  carry  off  the  static  charge  held  back  by  £he  choke  coil. 

Lightning  arresters  connected  with  line  wires;  practically  are  condensers 
of  small  capacity,  and  in  proportion  to  this  capacity  present  conducting 
paths  to  earth  for  alternating  currents. 

After  each  lightning  storm  it  is  well  to  inspect  all  open-type  carbon  block 
arresters  and  to  clean  away  any  deposit  of  carbon  dust  which  may  have 
accumulated  on  the  faces  of  the  blocks  or  on  the  mountings. 

LOCATION  OF  LIGHTNING  ARRESTERS 

Undoubtedly,  the  most  desirable  location  for  lightning  protectors  is 
outside  of  buildings,  but  owing  to  the  close  regulation  practised  and  to  the 
fact  that  the  instruments  and  apparatus  protected  must  be  safeguarded  from 
all  high-tension  currents  extraneous  to  the  buildings,  it  is  customary  to 
locate  arresters  inside  the  building. 

Outside  or  "pole"  arresters  in  various  forms  are  used  as  additional 
safeguards,  and  it  is  good  evidence  of  the  efficiency  of  these  external  pro- 
tectors that  the  number  of  instances  are  few  where  lightning  and  contact 
with  high-tension  circuits  result  in  fire  damage  to  buildings. 

Figure  97  shows  one  method  of  attaching  a  lightning  ground-wire  to  a 


LIGHTNING  AND  LIGHTNING  ARRESTERS 


125 


pole.  With  this  arrangement  a  double-grooved  insulator  is  required.  The 
wire  in  contact  with  the  ground  is  fastened  along  the  length  of  the  pole  by 
means  of  staples,  and  at  its  upper  extremity  is  twisted  around  the  upper 
groove  as  shown  on  the  right,  the  end  of  the  wire  being  bent  so  as  to  form  a 


.Ground 
Wire 


hook  with  which  to  clasp  the  bottom  of  the  insulator.  As  shown  on  the 
left,  a  space,  or  air-gap,  which  may  be  regulated  to  suit  the  requirements, 
separates  the  tie-wire  from  the  ground-rod. 


Compound 

-  D- Screw 

•Contact 
\;-Bfock 

-  Separator 

Block 
Contact 

•D- Screw 


W.FComp. 


FIG.  98.— The  "Brach"  pole  arrester. 

A  cross-section  view  of  the  Brach  arrester  adapted  to  out-door  service 
is  illustrated  in  Fig.  98.  The  manner  in  which  this  arrester  is  attached  to  the 
line  wire  is  illustrated  in  the  reproduction,  Fig.  99. 

When  new  lines  are  constructed,  one  telegraph  company  requires  that : 


126 


AMERICAN  TELEGRAPH  PRACTICE 


"About  10  ft.  of  line  wire  be  formed  into  a  flat  coil,  and  placed  under  the  butt 
of  the  pole.  The  other  end  of  the  wire  must  be  stretched  up  the  pole  and  fastened 
thereto  by  twelve  or  more  wire  staples.  It  will  be  extended  7  in.  above  the  top  of 
the  pole,  and  the  end  of  the  wire  will  then  be  turned  back  and  fastened  to  the  pole, 
making  a  projection  above  top  of  the  pole  3  in.  in  length  and  doubled  back,  the 
said  projection  to  be  given  three  turns  or  twists." 

Practice  in  regard  to  the  spacing  of  lightning  ground-wires  along  a  line 
varies  somewhat.  One  company  requires  that  a  ground  wire  be  attached  to 
every  fifth  pole,  while  another  company  requires  that  a  wire  be  attached  to 
every  sixth  pole  on  leads  carrying  from  i  to  12  wires,  35  poles  per  mile, 
and  on  lines  carrying  12  wires  or  upward,  with  more  than  35  poles  per  mile, 
the  ground-wire  must  be  attached  to  every  tenth  pole. 


FIG.  99. 

Fuses. — Protection  of  apparatus  against  abnormal  currents,  or  currents 
of  excessive  strength,  is  usually  accomplished  by  the  employment  of  properly 
designed  fuses. 

In  determinating  the  capacity  of  a  fuse  to  be  used  in  a  given  case,  the 
principal  points  to  be  considered  are: 

1.  The  amount  of  current  the  fuse  must  carry  continuously  under  nor- 
mal working  conditions. 

2.  The  amount  of  current  which  the  wiring  or  windings  of  the  apparatus 
can  safely  carry  during  a  certain  period  without  undue  heating. 

3.  The  possible  sources  of  trouble  from  foreign  circuits  carrying  high 
potentials. 

When  these  requirements  have  been  determined  with  reasonable  accuracy, 
the  carrying  capacity  of  the  fuse  may  be  decided  upon.  In  every  conductor 


FUSES 


127 


there  is  a  point  above  which  the  temperature  must  not  be  allowed  to  rise, 
and  the  customary  method  of  protecting  against  excessive  temperature  is  to 
employ  a  fuse  which  has  been  designed  to  "melt"  when  that  point  has  been 
reached. 

Ordinarily,  fuses  consist  of  short  lengths  of  wire  composed  of  an  alloy 
of  lead  and  tin.  The  wire  employed  for  the  purpose  may  be  of  any  desired 
diameter  and  length,  its  dimensions  depending  upon  the  degree  of  heat 
required  to  melt  it  when  excessive  currents  flow  through  the  conductor  of 
which  the  fuse  forms  a  part,  during  a  given  period  of  time. 

The  capacity  of  fuses  used  in  telegraph  circuits  ranges  from  1/2  to  10 
amperes,  with  intermediate  steps  of  i  ampere,  2  amperes,  and  so  on. 

The  half-ampere  fuse  generally  employed  will  "blow"  within  two  or  three 
seconds  after  being  subjected  to  a  current  of  i  ampere  at  75°  F. 

Owing  to  variations  in 
temperature  in  different 
parts  of  the  country,  be- 
tween winter  and  summer 
seasons,  it  has  not  been 
found  practicable  to  adjust 
the  blowing  point  of  1/2-  FlG  I00._Enclosed  fuse. 

ampere    fuses   much    closer 

than  that  indicated  above.  To  adopt  fuses  of  greater  capacity  than  those 
named,  for  telegraph  circuits,  would  place  such  circuits  in  the  category  of 
electric-light  wires,  which  would  be  manifestly  unreasonable,  as  the  regular 
operating  currents  in  telegraph  circuits  are  infinitesimal  when  compared 
with  the  large  currents  carried  in  lighting  circuits. 

In  the  construction  of  fuses,  several  different  types  of  fuse-link  are  used. 
These  might  be  classified  as  "straight-wire  link,"  "air-drum  link,"  "flat 
link,"  "multiple-link,"  "cylinder  link,"  etc. 


FIG.  1 01. — Air-drum  fuse  links. 

The  "enclosed"  fuse,  such  as  that  illustrated  in  Fig.  100,  consists  of  a 
pasteboard  tube,  containing  a  non-combustible  filling,  in  the  center  of  which 
is  stretched  the  fuse-link,  or  wire,  each  terminal  being  securely  connected 
with  brass  or  copper  ferrules  affixed  to  the  end  of  the  tube.  The  straight- 
wire  link  consists  simply  of  a  short  length  of  fuse-wire  of  uniform  diameter. 

In  the  construction  of  the  air-drum  link  (Fig.  101)  advantage  has  been 


128 


AMERICAN  TELEGRAPH  PRACTICE 


FIG.  102. — Mica  enclosed  fuse. 


taken  of  the  fact  that  the  blowing  time  of  a  fuse  may  be  rendered  practically 
constant  for  any  predetermined  overload,  regardless  of  the  temperature  of 
the  filling,  by  enclosing  a  section  of  the  fuse-wire  in  an  air-tight  casing. 

In  the  simpler  form  of  fuse  the  porous  filling  completely  envelops  the 
wire  throughout  its  length,  and  it  has  been  found  that  the  blowing  time 
varies  considerably  due  to  the  fact  that  the  material  of  which  the  filling 
consists  dissipates  the  heat  generated  in  the  fuse-wire,  which  to  an  appre- 
ciable extent,  makes  the  blowing  time  of  the  fuse 
dependent  upon  the  temperature  of  the  filling. 
The  air-drum  link  is  more  regular  in  action, 
owing  to  the  fact  that  the  air  space  around  a 
portion  of  the  fuse  metal  permits  of 'a  more 
definite  relation  between  the  temperature  of 
the  fuse-wire  and  the  current  value  in  the  circuit.  The  other  types  of 
fuse-link  mentfoned  are  modifications  of  the  two  described. 

The  filling  used  in  packing  the  fusable  element  must  be  non-combustible, 
and  preferably  should  be  non-absorptive  of  moisture,  chemically  inert, 
porous,  and  have  no  tendency  to  solidify. 

Figure  102  shows  a  form  of  "fuse"  wherein  a  short  length  of  fuse  metal 
is  enclosed  between  two  strips  of  mica,  the  fuse  element  being  stretched 
between  two  flat  copper  terminals  which  may  be  inserted  between  spring 
clips,  or  held  fast  by  cross  screws  extending  through  the  "slot"  ends. 

Figure  103  shows  a  convenient 
method  of  mounting  a  number  of  fuse 
units  such  as  that  illustrated  in  Fig.  102. 
When  mounted  in  a  box  as  shown,  one 
terminal  of  each  fuse  is  connected  to  a 
metal  strip,  which  in  turn  may  be  con- 
nected with  a  battery  or  other  source  of 
e.m.f.  while  the  other  terminal  of  each 
fuse  may  be  connected  to  any  circuit 
required  to  be  fed  from  that  particular 
battery. 

Ground-wires,   or  Earths. — When  a 

material  such  as  dry  wood,  fiber,  or  glass  is  filled  with  earth,  and  the  por- 
tion of  earth  thus  isolated  used  as  a  section  of  an  electric  circuit,  it  is  found 
that  the  resistance  of  the  earth  follows  the  same  laws  as  that  of  any  other 
substance,  or  the  ohmic  resistance  of  the  isolated  section  of  earth  depends 
upon  the  character  of  the  earth  employed,  the  amount  of  moisture  it  con- 
tains, and  upon  its  length  and  cross-section. 

When  two  metal  plates  are  buried  in  the  earth,  the  resistance  of  that 
portion  of  the  earth  extending  between  them  does  not  vary  in  the  ratio  of 
their  distance  apart  as  it  does  in  the  case  of  a  portion  of  earth  enclosed  in  an 


FIG.  103. — Box  for  mounting  mica  fuses. 


box   constructed   of   insulating 


GROUND  WIRES,  OR  "EARTHS"  129 

isolated  box.  The  resistance  between  two  separated  ground  plates  is  depend- 
ent upon  the  character  of  the  soil  in  the  immediate  neighborhood  of  each 
plate,  upon  the  depth  to  which  the  plates  are  buried  in  the  earth,  and  upon 
the  size  of  plate  used. 

On  account  of  the  large  surfaces  exposed  to  the  earth,  water-pipes,  and 
gas-mains  make  excellent  "earth"  connections.  Where  such  pipes  are  not 
available,  satisfactory  ground  connection  can  be  had  in  moist  earth  or  in 
a  river  which  does  not  flow  a  long  distance  in  a  channel  of  rock.  A  sheet 
of  zinc,  or  tinned  copper,  about  tV  in.  thick  and  about  4  ft.  square  should 
be  buried  in  a  hole  or  trench,  made  deep  enough  to  reach  below  dry  sand  or 
earth,  and  of  rock.  The  bottom  of  the  trench,  which  must  be  where  the 
earth  is  always  moist,  should  have  a  layer  of  coke  about  2  ft.  deep  on  which 
the  metal  plate  is  to  rest,  and  above  the  plate  should  be  deposited  a  layer 
of  crushed  coke  about  2  ft.  thick,  after  which  the  trench  should  be  filled  up 
with  moist  earth.  Connection  with  the  earth  plate  should  consist  of  a  hard- 
drawn  copper  wire  of  a  size  not  less  than  No.  9  B.  &  S.  gage,  the  earth  end 
being  soldered  entirely  across  the  surface  of  the  ground  plate. 

When  gas-pipes  or  water-pipes  are  used  in  place  of  buried  earth  plates, 
the  connection  should  be  made  by  wrapping  a  number  of  turns  of  the  ground- 
wire  around  the  pipe,  thoroughly  soldering  the  joint.  Connections  made 
to  pipes  should  invariably  be  made  on  the  "street"  side  of  all  service  taps, 
to  avoid  as  far  as  possible  interruptions  to  the  ground  connection  when 
changes  or  repairs  are  being  made  in  the  pipe  systems. 


CHAPTER  IX 

MAIN-LINE  SWITCHBOARDS  FOR  TERMINAL  OFFICES 
AND  INTERMEDIATE  OFFICES 

At  an  office  where  a  " one- wire"  line  terminates,  the  only  circuit  access- 
ories required  in  addition  to  the  signaling  instruments  are  a  lightning  ar- 
rester, a  line  "fuse,"  and  a  "ground"  connection.  In  order  that  the  signal- 
ing relay  may  be  "cut  out,"  that  is,  disconnected  from  the  line,  during  the 
absence  of  the  attendant,  or  on  any  other  occasion  when  such  action  might 
be  desirable,  it  is  usual  to  embody  a  "cut-out"  feature  in  the  lightning 
arrester  and  ground-switch  unit.  A  simple  form  of  this  type  of  apparatus 
is  illustrated  in  Fig.  91.  This  same  device  would  answer  all  the  require- 
ments of  an  "intermediate"  office  on  a  single-wire  line. 

Where  two  or  more  line  wires  are  cut  into  an  intermediate  office,  or 
terminate  at  an  office,  then,  in  addition  to  the  features  above  mentioned,  a 
means  must  be  provided  whereby  any  two  wires  may  be  quickly  cross-con- 
nected, or  looped.  Also  a  means  should  be  provided  whereby  any  one  of 
the  various  line  wires  may  be  connected  to  any  one  of  several  sets  of  signal- 
ing instruments  or  to  several  sets  of  instruments  at  the  same  time. 

From  an  operating  standpoint,  the  importance  of  a  telegraph  office  is 
closely  related  to  the  extensiveness  of  the  switching  facilities  necessary  to 
carry  on  the  work  of  the  office,  and  of  the  "wire  district"  in  which  the  office 
is  situated. 

On  account  of  the  constantly  changing  conditions,  it  is  rather  difficult 
to  classify  telegraph  offices  in  an  order  that  would  predetermine  the  appa- 
ratus required  to  equip  any  particular  office.  For  general  purposes,  how- 
ever, it  is  possible  to  gain  a  helpful  understanding  of  the  requirements  in  a 
given  case,  where  offices  are  classified  as  follows: 

Branch  Offices,  meaning,  in  a  city,  branches  from  the  main  office. 

Way  Offices,  small  intermediate  offices,  cut  in  on  one-,  two-,  or  three-way 
wires,  operated  simple  Morse. 

Intermediate  Test  Office. — An  office  on  a  trunk  line  having  all  through 
wires  cut  in  for  testing  purposes. 

Repeater  Station. — An  office  on  a  trunk  line  where  signals  are  automatically 
repeated,  from  one  section  to  another  on  some  or  all  of  the  wires  connected 
into  the  office. 

Terminal  Station. — Offices  located  in  large  centers,  where  a  considerable 
volume  of  local  telegraphic  traffic  is  handled,  where  messages  are  relayed 

130 


MAIN-LINE  SWITCHBOARDS 


131 


by  hand,  to  other  points,  where  automatic  repeating  facilities  are  available, 
and  where  "battery"  is  applied  to  main-line  wires  radiating  therefrom. 

A  more  extended  classification  would  mean  the  subdivision  of  each  of 
these  classes  into  several  grades,  and  the  governing  factors  would  include 


UN£S  &  LOO  PS 


FUSES 
/OO  M/LS  M/DA 


SOUNDER 


SWITCHBOARD  EQU/PMENT 

AND  STRAP  BOARDS 

FIG.  104. 


the  amount  of  business  handled,  whether  or  not  main-line  wires  take  battery 
at  the  office,  whether  main-line  testing  is  done  from  the  office,  etc. 

Where  the  design  of,  and  the  operation  of  the  switching  apparatus  are 
concerned,  it  is,  of  course,  quite  desirable  to  employ  standard  apparatus. 


132 


AMERICAN  TELEGRAPH  PRACTICE 


The  continual  improvement  being  made  in  the  design  and  construction  of 
switchboard  equipment  means  that  standardization  and  improvement  must 
go  hand  in  hand,  and  the  benefits  are  best  secured  when  improvements  are 
introduced  gradually  throughout  the  entire  system. 

A  type  of  main-line  switchboard  formerly  known  as  the  Universal,  now 
generally  referred  to  as  the  strap-and-disk  board,  has  for  many  years  been 
extensively  employed  at  both  intermediate  and  terminal  stations. 

Figure  104  gives  a  diagrammatic  view  of  the  electrical  connections  between 
line  wires  and  office  instruments  'where  a  strap-and-disk  switchboard  is 
used.  Two  separate  line  wires  are  shown  "looped"  into  the  office,  both 

J-,  JL 

r"w  rw 


JL  ^       JLJL       U-.JL 

:,w  e  w       ^wew        e,  w  e  v 

\__/ 

*-*. 

*-* 

-      6- 

S—/* 

^  —  ( 

^ 

H      6- 

s  | 

\  —  f 

.  1 

k  ( 

\—* 

\_-.y 

:< 

^-H 

*i     < 

\—f 

»  —  ' 

\  f 
\  1 

^ 

X—/1 

\—f 

>  —  ( 

^  ' 

^H 

\__y 

^ 

">  —  ^ 

FIG.  105. 


FIG.  106. 


FIG.  107. 


FIG.  108. 


w  8  w 


w  E  w 


FIG.  109.  FIG.  no.  FIG.  in. 

FIGS.  105  to  in. — Strap-and-disk  switchboard  combinations. 

sides  of  each  loop  being  connected  through  2o-ampere  fuses,  and  to  a  lightning 
arrester  having  a  separation  between  line  and  ground  plates,  of  one  tenth  of 
an  inch.  It  is  evident  that  the  "board"  shown  in  Fig.  104  has  accommoda- 
tion for  four  through  wires,  that  is,  four  line  wires  may  be  looped  into  an 
office  having  a  board  of  this  size. 

The  vertical  elements  or  " straps"  are  connected  with  either  side  of  a 
line,  and  each  pair  of  straps  in  use  represent  one  external  circuit  connected 
into  and  out  of  the  office,  while  the  horizontal  elements,  the  disks  (which 
are  connected  together  in  horizontal  rows  by  means  of  metallic  strips  on  the 
back  of  the  board)  are  by  way  of  binding  posts  connected  through  half-ampere 


MAIN-LINE  SWITCHBOARDS 


133 


fuses,  and  lightning  arresters  having  a  o.oi- 
in.  gap  between  plates,  to  signaling  relays 
mounted  on  the  operating  tables. 

Figures  105  to  in  inclusive  show  various 
combinations  which  may  be  made  at  an  in- 
termediate office,  with  two  through  circuits, 
extending,  say  east  and  west  of  the  office. 

Figure  105  shows  the  horizontal  elements 
and  the  vertical  elements  of  the  switchboard, 
so  connected  by  means  of  metallic  "pegs" 
that  each  circuit  is  connected  through  the 
office,  including  in  one  circuit  the  signaling 
relay  connected  with  binding  posts  A ,  and  in 
the  other  circuit  the  relay  connected  with 
posts  B. 

Figure  106  shows  wire  No.  i  west  "  cross- 
connected"  with  wire  No.  2  east,  and  wire 
No.  i  east  with  wire  No.  2  west;  each  circuit 
so  made  up  includes  the  windings  of  the  sig- 
naling instrument  wired  to  the  terminals  A 
and  B,  respectively. 

If  it  is  desired  to  eliminate  the  winding  of 
the  instrument  connected  with  posts  A  from 
the  circuit  in  which  it  is  connected,  all  that  is 
necessary  is  to  place  the  two  center  pegs  in 
the  positions  indicated  in  Fig.  107.  Simi- 
larly, instrument  B  may  be  eliminated  from 
the  circuit  as  shown  in  Fig.  108,  and  both 
instruments  may  be  cut  out  if  the  pegs  are  in- 
serted as  shown  in  Fig.  109.  A  horizontal 
row  of  disks  is  assigned  to  the  ground  con- 
nection G,  and  any  wire  may  be  "grounded" 
simply  by  inserting  a  peg  in  the  hole  at  the 
intersection  of  the  vertical  strap  connected 
with  the  wire  to  be  earthed. 

Figure  no  shows  the  disposition  of  the 
pegs  when  it  is  desired  to  "loop"  wire  No.  i 
east  with  wire  No.  2  east,  allowing  the  instru- 
ment A  to  remain  in  circuit,  or  if  it  is  not  re- 
quired to  have  the  home  instrument  cut  in,  FlG.  II2._Improvedformof  strap- 
the  pegs  should  be  inserted  as  in  Fig.  in.  and-disk  switchboard. 

Switchboards  of  this  type  may  be  built 
large  enough  to  take  care  of  any  number  of  wires.  It  is  evident,  of  course, 


O 


O 


134 


AMERICAN  TELEGRAPH  PRACTICE 


that  as  a  board  is  enlarged  to  accommodate  a  large  number  of  wires,  its 

dimensions  increase  in  both  directions;  that  is,  vertically  and  horizontally. 

One  difficulty  experienced  with  the  strap-and-disk  switchboard  is  that  the 

pegs  are  liable  to  work  loose,  and  result  either  in  a  poor  contact  between 


to  AM  P.  Fuses. 

tOO/M/LS 


FIG.  113. — Cross-bar  main-line  switchboard. 

strap  and  disk  (thus  introducing  an  abnormally  high  resistance  into  the 
circuit)  or  fall  out  entirely  and  interrupt  the  circuit.  This  difficulty  is  more 
often  encountered  in  offices  located  in  railroad  depots  where  vibration 
caused  by  passing  trains  in  time  causes  the  pegs  in  the  switchboard  to  work 
loose. 


MAIN-LINE  SWITCHBOARDS 


135 


To  avoid  this  annoyance  an  improved  form  of  strap-and-disk  board  has 
recently  been  brought  out  (Fig.  112)  the  construction  of  which  provides  for 
a  more  positive  union  between  peg,  disk  and  strap.  Instead  of  the  tapered 
pegs  usually  employed,  the  improved  board  has  a  straight  peg  which  goes 
through  a  hole  drilled  all  the  way  through  the  slate  or  abestos  board 


FIG.  114. — Double-conductor  plugs  for  use  with  cross-bar  switchboard. 

base,  and  engages  spring  clips  which  are  fastened  to  the  backs  of  the  disks 
and  straps. 

A  form  of  switchboard  known  as  the  " cross-bar"  board,  in  use  at  many 
offices,  is  illustrated  in  Fig.  113.  In  principle  this  form  of  switchboard  is 
identical  with  the  more  common  strap-and-disk  board.  All  of  the  combina- 
tions possible  with  the  latter  may  be  made  with  the  cross-bar  arrangement. 
The  only  noteworthy  difference  being  that  the  home  relay  is  connected  into 
the  desired  circuit  by  means  of  a  "  double-plug, "  which  completes  the  circuit 
from  horizontal  strip  through  the  double- 
conductor  cord  and  back  to  the  vertical  strip. 
When  it  is  not  required  to  have  the  home 
relay  in  circuit,  a  solid  plug  is  inserted  in 
place  of  the  double-plug.  The  diagram, 

Fig.  113,  shows  the  fuse,  lightning  arrester,  FlG' 

,  ,  , .  ,        ,  . 

and  ground  connections,  also  the  connections 

of  the  main-line  and  local  instruments  required  in  connection  with  this 
type  of  switchboard. 

It  is  evident,  too,  that  for  a  given  number  of  vertical  straps,  the  cross-bar 
form  of  switchboard  will  accommodate  twice  as  many  lines  connected 
through  an  intermediate  office  as  will  the  strap-and-disk  board,  owing  to  the 
fact  that  the  lines  in  one  direction  are  connected  to  the  vertical  straps  and 
the  lines  in  the  opposite  direction  to  the  horizontal  straps,  or  bars. 

Figure  114  illustrates  the  form  of  double  plug  used  with  the  cross-bar 
board  to  cut  in^  set  of  instruments.  The  cord  used  in  connection  with  this 
plug  is  a  flexible  double  conductor,  one  conductor  being  connected  with  the 
"tip"  of  the  plug,  while  the  other  is  connected  with  the  metal  portion  of  the 
plug  back  of  the  hard-rubber  insulating  strip. 


ii5- — Split  plug  for  use  with 
strap-and-disk  switchboard. 


136 


AMERICAN  TELEGRAPH  PRACTICE 


The  strap-and-disk  board,  also,  may  be  connected  so  that  the  lines  extend- 
ing in  one  direction  will  be  attached  to  the  binding-post  terminals  of  the 
horizontal  elements,  while  the  lines  in  the  opposite  direction  will  be  attached 
to  the  vertical  straps.  When  this  is  done,  a  " split-plug"  of  the  form  shown 
in  Fig.  115  is  used  to  cut  in  a  set  of  instruments  at  the  home  station.  Where 
switchboards  are  wired  in  this  way,  it  is  necessary  to  have  one  or  two  spare 


JL_ 


FIG.  116. — Double  porcelain  base  spring-jack. 

horizontal  and  as  many  spare  vertical  straps  in  order  that  line  wires  may  be 
"looped"  when  required. 

The  unit  type  of  strap-and-disk  switchboard  illustrated  in  Fig.  112,  in 
connection  with  the  spring-jack  arrangement  shown  in  Fig.  116,  has  within 
recent  years  been  introduced  for  the  purpose  of  meeting  the  need  for  a  more 
flexible  and  rapid  switching  system. 


FIG.  117. — Single  and  double  conductor  wedges  for  use  with  spring-jacks. 

The  "wedges"  (Fig.  117)  used  in  connection  with  spring-jacks  to  make 
the  various  combinations  of  circuits  required  in  practice  are  made  up  either 
as  single  conductors  or  as  double  conductors.  The  "single"  wedge  has  a 
length  of  flexible  single-conductor  cord  attached  to  a  brass  strip  on  one  side 
of  the  wedge,  the  other  side  of  which  is  of  hard  rubber,  while  the  "double" 
wedge  has  a  brass  strip  on  each  side,  separated  by  an  insulating  strip  of  hard 
rubber.  Each  of  the  metal  strips  has  connected  with  it  one  of  the  conduct- 
ors of  a  flexible  twin-cord. 

The  spring- jack,  permitting  as  it  does  of  the  insertion  of  several  wedges 


MAIN-LINE  SWITCHBOARDS 


137 


in  various  relations  to  each  other,  provides  an  excellent  means  of  meeting 
main-line  telegraph  switchboard  requirements. 

Figure  118  shows  a  front  and  a  side  view  of  one  unit  of  the  arrangement 
referred  to.     The  line  wires  are  shown  entering  through  the  "fuse"  and 


FIG.  1 1 8. — Front  and  side  views 
of  switchboard  unit  including  strap 
and  disk,  and  spring-jack  connections. 


FIG.  119. 


lightning  protector,  from  there  connected  to  the  inside  or  stationary  element 
of  the  spring-jack,  the  spring-actuated,  or  movable  element  (the  shank)  of 
which  is  in  turn  connected  with  a  vertical  strip  of  the  switchboard  proper. 
Figure  119  shows  the  back-of-the-board  wiring  of  a  five-line  intermediate 


138 


AMERICAN  TELEGRAPH  PRACTICE 


switchboard  of  the  strap-and-disk  type  equipped  with  spring-jacks.  It 
may  be  noted  that  the  connecting  wires  leading  from  the  office  side  of  the 
protective  device  to  the  heel  of  the  spring-jack,  are  "cabled"  instead  of 
being  brought  down  separately  as  shown  in  Fig.  118.  The  lower  portion 


FIG.  120. 

of  Fig.  119  plainly  shows  the  theory  of  the  connections  of  this  convenient 
switching  arrangement. 

One  of  the  advantages  of  the  unit  type  of  board  is  that  the  switching 
facilities  of  an  office  may  be  increased  to  take  care  of  additional  lines,  simply 
by  adding  additional  units  to  the  existing  switchboard. 

Several  years  ago  telegraph  engineers  recognized  the  possibilities  of  the 


MAIN-LINE  SWITCHBOARDS 


139 


telephone  type  of  jack  (the  pin-jack)  for  telegraph  purposes,  and  the  pioneer 
work  along  this  line,  done  by  Mr.  J.  F.  Skirrow,  Associate  Electrical  Engineer 
of  the  Postal  Telegraph- Cable  Company,  New  York,  has  resulted  in  the 
development  of  a  line  of  switching  apparatus  which  embodies  all  of  the  ad- 
vantages of  this  compact  and  useful  device.  Pin-jacks  are  made  to  meet 
various  requirements,  and  are  known  as  "  open-circuit  jacks,"  "  closed- 
circuit,"  "patching,"  "grounding,"  "series,"  "multiple"  jacks,  etc.  In 
construction,  several  of  these  forms  of  jack  are  identical,  but  the  different 
forms  are  variously  designated  as  stated. 


Several  of  these  Blocks  may  be  used 
together  where  Cut-outs  on/y,  withouf 
Switching  Facilities  are  required. 


Looping    Cord 
for  Connecting  "Line"  to  "Table*. 


Main  LineSounder,  K.O.  B. 


\5dr. 


FIG.  121. 


Figure  120  shows  several  styles  of  pin-jack,  each  designed  to  meet  a 
different  requirement.  If  in  each  case  the  dark  sections  are  regarded  as 
consisting  of  insulating  material,  the  uses  to  which  each  may  be  put  is  self- 
evident.  No.  i,  for  instance,  is  a  series  or  closed-circuit  jack  intended  for 
use  in  a  wooden  shelf.  No.  2,  a  series  or  closed-circuit  jack  for  use  in  a 
porcelain  block.  No.  3,  an  open  or  multiple-jack  for  use  in  a  wooden  shelf. 
No.  4,  an  open  jack  for  mounting  in  a  porcelain  block.  Nos.  5  and  6 ,  patching 
jacks  for  mounting  in  wood  and  porcelain  respectively. 

Figure  121  shows  a  switch  "block"  having  the  line  and  instrument 
circuits  connected  through  pin-jacks.  The  pin-jacks  are  mounted  in  a  porce- 
lain block  on  a  common  base  with  the  fuse  holders  and  the  lightning  arresters. 


140 


AMERICAN  TELEGRAPH  PRACTICE 


• 


Line 

^Arrester 


Figure  122  shows  the  theoretical  connections  of  the  five  pin-jacks.  It 
will  be  seen  that  the  two  "line"  and  two  "table"  jacks  are  of  the  closed- 
circuit  or  series  type,  while  the  grounding-jack  is  of  the  open-circuit  type. 

The    insertion   of  a  solid  metal 

«plug  in  the  grounding-jack  connects 

!j^  the    line  wires    to   "earth"  on  the 

||j      ground  side  of  either  line- jack,  while 
aa_=====L         j^^     n      Adi       tne    insertion    of    double-conductor 
[T^^— '-Jl         iP^ss^n     ^||        ,          ,  ,  ,        .  .      .     „. 

1  Line  li-L-Jj  Line        |      PluSs   (sh°wn  on  the  right  in  Fig. 

121)  in  either  of  the  line-jacks  con- 
nects the  line  in  series  with  which- 
ever table-jack  the  double  plug  on 
the  other  end  of  the  flexible  cord  may 
be  inserted  into. 

FIG.  122.— Connections   of    the  five  pin-          The  mam_line  instruments  in  the 
jacks  mounted  in  the  switch  block.  Fig.  121.      „.  Al         .      ,    ,      ,, 

office  are  permanently  wired  to  the 

binding-posts  on  the  lower  edge   of  the  switch-block,  the  binding-posts, 
in  turn,  being  connected  with  the  table-jacks. 

It  is  evident  that  provision  is  made  for  operating  one  or  two  main -line 


Line 
Arrestrl 


FIG.  123. — Switch  block  equipped  with  cross-connecting  facilities. 


MAIN-LINE  SWITCHBOARDS 


141 


instruments  upon  a  "loop,"  and  also  for  "splitting"  or  dividing  the  loop 
into  two  single  grounded  circuits,  the  latter  being  accomplished  by  the 
insertion  of  a  solid  metal  plug  in  the  ground-jack. 

This  switching  arrangement,  however,  cannot  be  used  where  cross- 
connecting  facilities  are  required. 

As  a  branch  office  "cut-out"  this  arrangement  meets  the  requirements 
-admirably.  When  the  office  instruments  are  to  be  cut  out  at  night,  the 
only  operation  necessary  on  the  part  of  the  attendant  is  to  withdraw  the 
plugs  from  the  pin-jacks. 

A  switch-block  similar  to  the  above  in  construction  and  appearance, 
but  having  facilities  for  cross-connecting  wires,  is  depicted  in  the  diagram, 
Fig.  123. 

Intermediate  switchboards  intended  for  several  wires  may  be  made  up  by 
assembling  a  number  of  these  units. 

To  ground  a  wire  in  either  direc- 
tion, a  solid  metal  plug  is  inserted  in 
the  ground-jack.  Cross-connections 
are  made  by  means  of  flexible  con- 
ducting-cords  having  solid  metal 
plugs  on  each  end.  One  plug  is  in- 
serted in  the  patching-jack  of  one 
wire  and  the  other  plug  in  the  patch- 
ing-jack of  the  other  wire,  east  or 
west,  north  or  south,  as  desired. 

To  test  a  patch  by  grounding 
the  line,  one  plug  of  a  patching-cord 
is  held  in  contact  with  the  ground-post  below  the  lightning  arrester,  while 
the  other  plug  is  held  in  contact  with  the  line  wire  where  it  enters  the  fuse. 
The  office  instruments  may  be  cut  in  through  the  looping-jacks  by  means 
of  the  double-conductor  cords  and  plugs  shown  on  the  right  and  left, 
Fig.  123. 

Figure  124,  shows  theoretically  the  connections  through  the  various 
jacks. 

These  switch-blocks  are  fire-proof  and  practically  indestructible. 

In  most  of  the  offices  of  the  Western  Union  Telegraph  Company,  and  in 
the  majority  of  railroad  offices  throughout  the  United  States  and  Canada, 
the  strap-and-disk  switchboard  is  used  at  intermediate  offices.  In  the 
offices  of  the  Postal  Telegraph- Cable  Company,  as  well  as  in  the  railroad 
offices  operated  in  connection  with  the  Postal  Company's  system,  although 
there  are  a  large  number  of  strap-and-disk  switchboards  in  use,  the  pin-jack 
type  of  switch  is  extensively  employed,  and  such  equipment  is  regarded  as 
standard. 

At  intermediate  offices  having  not  over  six  main  wires,  the  "Postal" 


FIG.  124. — Connections  of  the  five  pin-jacks 
mounted  in  the  switch  block,  Fig.  123. 


142 


AMERICAN  TELEGRAPH  PRACTICE 


employs  a  switching  system  made  up  as  shown  in  Fig.  125.  In  the  diagram 
is  shown  all  necessary  circuit  equipment  for  six  through  wires.  The  view 
at  the  top  shows  the  course  of  the  circuit  from  where  the  line  wire  enters 
from  the  west  through  the  pin-jack  contacts  and  fuses  to  the  point  where  the 
line  east  leaves  the  office. 

The  lightning  arrester  and  fuse  equipment  in  each  case  is  mounted  on 
separate  porcelain  blocks.  Also,  the  six  pin-jacks  are  mounted  in  a  porce- 
lain block.  Thus  each  wire  connected  into  and  out  of  the  office  passes 
through  a  three-block  unit  consisting  of  two  fuse  and  arrester  blocks  and  a 
pin-jack  block.  Two  of  the  jacks  are  looping-jacks,  one  to  cut-in  east,  the 
other  to  cut-in  west.  Two  of  the  jacks  are  patching-jacks  east  and  west, 


it/era***  BfrouGt/T  THirovfftt  uuc  Ft/sea. 

FIG.  125. — Pin-jack  switchboard  equipment  for  offices  having  not  over  six  lines. 

and  the  remaining  two  are  grounding-jacks  east  and  west.  Where  this 
type  of  switchboard  is  used,  the  following  directions  apply  to  its  operation  : 

To  Cut  in  or  Loop  an  Instrument  upon  a  Wire.— Place  the  instrument 
plug  in  one  of  the  jacks  of  the  wire  it  is  desired  to  loop  into,  under  the  word 
"loop"  in  the  brass  guide  plate. 

To  Open  a  Wire. — Place  a  solid  plug  in  the  jack  of  the  wire  it  is  desired 
to  "open"  under  the  words  "open  or  patch"  in  the  guide  plate. 

To  Ground  a  Wire. — Use  the  same  plug  as  for  opening,  but  place  it  in 
the  jack  under  the  word  "ground"  in  the  guide  plate.  If  a  grounding- 
plug  and  an  opening-plug  are  used  upon  the  same  side  of  a  wire  at  the  same 
time,  the  wire  will  be  opened  upon  that  side  and  grounded  upon  the  other. 
Looping,  opening  or  grounding  may  be  done  north,  south,  east  or  west 
according  to  which  jack  of  the  two  provided  for  that  purpose  is  used,  in 
accordance  with  the  marks  on  the  guide  plate. 

To  Patch  a  Wire. — Use  a  cord  with  a  solid  plug  on  each  end.  If  it  is  de- 
sired to  patch  No.  i  west  to  No.  2  east,  place  one  plug  in  the  jack  No.  i  west 


MAIN-LINE  SWITCHBOARDS 


143 


under  the  words  "open  or  patch"  in  the  guide  plate  and  the  other  plug  in 
the  jack  No.  2  east  under  the  words  "open  or  patch."  All  other  patches 
are  made  in  a  similar  manner. 


JMCKS      \     JACKS 


lilll! 

Stiff*  3 


C/fOSS  CONNECTING  f?AC/f  ANO 
TE&M/NAL   BAR 


FIG.  126. — Pin-jack  switchboard  for  offices  having  six  or  more  through  wires. 

To  Connect  a  Loop  into  a  Main  Line. — Loops  are  brought  to  the  switch- 
board in  the  same  manner  as  line  wires,  that  is,  one  side  of  the  loop  comes 
in  at  each  side  of  the  board.  Use  a  double-cord  with  a  double,  or  "looping  " 


144  AMERICAN  TELEGRAPH  PRACTICE 

plug  on  each  end.  Place  one  plug  in  a  jack  of  the  loop  under  the  word 
"loop,"  and  the  other  plug  in  a  jack  of  the  line  under  the  word  "loop." 
Another  method:  use  single  cords  and  patch  one  side  of  the  loop  to  one  side 
of  the  line,  and  the  other  side  of  the  loop  to  the  other  side  of  the  line,  using 
the  patching  jacks  as  explained  under  "to  patch  a  wire."  When  neces- 
sary to  place  more  than  one  loop  upon  the  same  line,  connect  the  loops 
together,  using  a  double-cord  from  a  looping-jack  of  one  loop  to  a  looping- 
jack  of  the  other  loop.  Then  connect  the  line  to  one  of  the  loops  as  described 
above. 

When  an  attendant  is  asked  to  ground  a  wire  "out  side  of  the  board" 
for  a  test,  the  procedure  outlined  in  connection  with  Fig.  123  for  "testing 
a  patch  by  grounding  the  line"  may  be  followed. 

All  of  the  "fuse"  and  switchboard  connections  of  a  wire  can  be 
"bridged"  out  (to  test  fuses,  jacks,  etc.)  by  using  a  single  cord,  placing  one 
plug  against  each  of  the  line  terminals  at  the  fuse  blocks. 

A  double  plug  attached  to  a  double-conductor  cord  connected  with  the 
office  instrument  is  inserted  in  a  looping  jack  when  it  is  desired  to  cut  the 
instrument  in  circuit. 

At  intermediate  offices  having  six  or  more  through  wires,  in  those  in- 
stances where  pin-jack  equipment  is  used,  the  fuse  and  arrester  blocks, 
pin-jack  blocks,  etc.,  are  mounted  on  an  angle-iron  frame  of  substantial  con- 
struction and  finished  appearance  as  indicated  in  Fig.  126. 

The  circuit -connections  are,  of  course,  identical  with  those  shown  in  the 
smaller  switchboard,  Fig.  125.  To  the  larger  board  there  is  added  a  "ter- 
minal bar,"  and  a  cross-connecting  rack,  mounted  on  the  back  of  the  switch- 
board as  shown  on  the  right,  Fig.  126.  These  additional  features  make 
possible  a  systematic  distribution  of  cable  conductors  and  provide  means 
whereby  cross-connections  may  be  made  between  the  line  wires  on  the  back 
of  the  board  when  so  desired. 

TERMINAL  OFFICE  SWITCHBOARD  EQUIPMENT 

The  highest  development  in  switchboard  construction  is  found  at  the 
larger  terminal  stations,  where  on  account  of  the  large  number  of  lines  to  be 
cared  for,  it  is  necessary  to  employ  thoroughly  systematized  methods  of 
circuit  identification,  and  to  provide  facilities  for  making  alterations  and 
additions  to  the  wire  plant  in  such  a  manner  that  regular  service  will  not 
be  interrupted. 

Figure  127  shows  an  arrangement  of  fuse  and  arrester  equipment  at  a 
terminal  office.  The  line  wires  from  the  aerial  or  underground  cable  are 
shown  coming  from  the  street  in  a  cable.  Each  line  wire  has  a  circuit  through 
one  of  the  terminal  blocks,  to  the  cable  which  leads  to  the  cross-connecting 
frame  shown  on  the  left.  Usually  the  terminal  frame  shown  on  the  right  is 


MAIN-LINE  SWITCHBOARDS  FOR  TERMINAL  OFFICES     145 

located  as  near  as  possible  to  the  point  where  the  cabled  line  wires  enter  the 
building.  The  terminal  bars  mounted  in  this  frame  consist  of  porcelain 
blocks,  each  one  of  which  has  mounted  in  it  four  pin-jacks  as  shown  in  outline 


ooooooooooooooooooooo 


FIG.  127. 

at  the  top  of  the  frame.     These  pin- jacks  provide  a  means  whereby  "  ground- 
ing," "patching"  and  "looping"  may  be  done,  in  a  way  identical  with  that 
described  in  connection  with  the  smaller  intermediate  switchboards. 
10 


146 


AMERICAN  TELEGRAPH  PRACTICE 


MAIN-LINE  SWITCHBOARDS  FOR  TERMINAL  OFFICES     147 

The  cross-connecting  frame  shown  on  the  left  is  located  in  close  proximity 
to  the  main  switchboard  in  the  operating  room;  generally  it  is  convenient 
to  mount  the  frame  immediately  in  the  rear  of  the  switchboard. 

A  more  complete  plan  of  the  wiring  between  the  point  where  line  wires  are 
brought  from  the  terminal  room  to  the  fuse  and  arrester  frame  in  the  rear  of 
the  switchboard  proper,  and  the  cross-connecting  frame,  is  shown  in  Fig.  128. 
The  arrangement  of  conductors  from  cross-connecting  frames  to  pin- jacks 
and  spring- jacks  in  the  main  switchboard  and  from  cross-connecting  frames 
to  instrument  tables  is  clearly  shown  in  the  diagram.  The  pin-jack  locations 
A  provide  a  means  for  transferring  circuits  from  one  section  of  the  main 
board  to  other  sections.  All  of  the  connections  are  made  with  flexible 
conducting  cords  the  terminals  of  which  are  equipped  with  single  or  double 
plugs,  single  or  double  wedges  as  required. 

The  terminal  room  equipment  is  in  reality  a  switching  system,  practically 
a  duplicate  of  that  installed  in  the  main  operating  room,  but  constructed 
with  the  object  of  providing  for  flexibility  and  utility  rather  than  for  fine 
appearance.  The  advantages  of  having  a  complete  switching  system  close 
to  the  point  where  the  lines  enter  the  building  from  underground  and  aerial 
cables  are  that  the  jacks  in  the  terminal  room  frame  serve  both  for  cable 
terminals  and  for  temporary  cross-connecting  purposes  by  means  of  cords 
when  cables  are  in  trouble.  From  this  frame  may  be  made  quick  tests  of 
cable  interruptions,  and  the  equipment  may  be  used  as  a  temporary  switch- 
board in  case  the  main  switchboard  in  the  operating  room  should  be  de- 
stroyed by  fire  or  disabled  from  any  cause. 

The  function  of  the  cross-connecting  frame  mounted  in  the  rear  of  the 
main  switchboard  is  to  act  as  an  intermediate  connection  between  the  pin- 
jack  and  spring-jack  connections  of  the  switchboard  and  the  instruments 
located  on  operating  tables. 

In  the  offices  of  the  Postal  Telegraph-Cable  Company  all  frames  are  of 
angle-iron,  including  switchboard  frames  and  all  switchboard  connections, 
cross-connecting  frame,  and  terminal  frame  connections  are  mounted  either 
upon  slate,  porcelain,  or  asbestos  board. 

CONDUCTORS  BETWEEN  CROSS-CONNECTING  FRAMES  AND 
OPERATING  TABLES 

All  of  the  conducting  wires  required  between  cross-connecting  frames 
and  instrument  tables,  and  between  the  power  switchboard  and  instrument 
tables  are,  in  all  up-to-date  installations,  carried  through  floor  ducts  or 
trenches. 

The  trenches  are  from  4  to  8  in.  wide  and  of  about  the  same  depth,  and, 
as  usually  arranged,  have  a  conveniently  remcvable  cast-iron  top  or  lid,  laid 
flush  with  the  surface  of  the  floor.  In  this  trench  are  laid  all  of  the  battery 


148 


AMERICAN  TELEGRAPH  PRACTICE 


if 


o  n  n  n  n  n 


U   U  U  U   U  U 


MAIN-LINE  SWITCHBOARDS  FOR  TERMINAL  OFFICES     149 

wires  and  cables  leading  from  the  cross-connecting  frames  to  the  various 
operating  tables. 

In  some  instances,  instead  of  using  open  top  trenches,  iron  pipes  i\  in. 
in  diameter  are  embedded  in  concrete  flooring  and  so  distributed  that  all 
parts  of  the  operating  room  are  served  as  indicated  in  Fig.  129.  The  diagram 
shows  a  skeleton  main-line  switchboard  with  cross-connecting  frame  in  the 
rear.  An  iron-pipe  conduit  is  shown  laid  beneath  the  office  flooring  and 
stretching  from  the  wiring  frame  to  an  operating  table,  there  terminating  in 
a  hand-hole  with  surface  outlet  under  the  table.  From  the  hand-hole  a 


'Cable 


Transfers 


'ity  Loop 


FIG.  130. — Line  wire  connections  between  underground  or  aerial  cables  and  main-line 
switchboard  at  a  terminal  office. 

short  lateral  duct  provides-  access  to  the  instruments  mounted  on  top  of  the 
table  through  a  wire  chute  situated  between  the  type-writer  lockers. 

In  the  more  recent  installations  a  wiring  cabinet  has  been  built  into  the 
aisle  end  of  each  operating  table,  the  hand-hole  outlet  from  the  floor  duct 
being  built  in  the  floor  within  the  cabinet.  This  latter  arrangement  provides 
for  accessible  mounting  of  all  fuses,  resistance  coils,  cable  terminal  strips, 
etc.,  constituting  that  part  of  the  equipment  of  the  table. 

The  plan  and  construction  details  shown  in  Fig.  129  are  self-explanatory. 


150 


AMERICAN  TELEGRAPH  PRACTICE 


That  portion  of  the  wiring  of  a  terminal  office  between  the  cross-connect- 
ing frames  and  the  switchboard,  so  far  as  main-line  wires  are  concerned,  is 
shown  in  Fig.  130. 

The  course  of  a  line  wire  from  the  aerial  or  underground  cable  may  be 
traced  through  the  line  fuse,  lightning-arrester  block,  cross-connecting  wire 
to  terminal  bar,  thence  through  a  closed-circuit  or  series  pin-jack  to  the 
spring-jack  mounted  on  the  face  of  the  main  switchboard.  If  the  main- 
line wire  shown  is  regularly  assigned  to  a  particular  service,  the  connection 
is  made  by  means  of  a  short  flexible  cord  with  plug  terminals,  the  plugs 
being  inserted  in  the  pin-jacks  as  suggested  in  the  diagram.  The  employ- 
ment of  short  cords  for  regular  circuit  assignments  greatly  reduces  the 
amount  of  conducting  cord  necessary  to  make  a  given  number  of  connections. 


FIG.  131. — Sections  of  a  main- line  switchboard  at  a  terminal  office. 

If  the  line  wire  shown  were  required  to  be  transferred  to  a  distant  part 
of  the  board,  the  plug  on  one  end  of  the  cord  would  be  inserted  in  the  closed- 
circuit  jack,  while  the  other  plug  would  be  inserted  in  one  of  the  transfer- 
jacks  leading  to  that  section  of  the  switchboard  where  the  connection  is 
desired. 

Figure  131  shows  two  sections  of  a  large  main-line  switchboard  built  up  of 
slate  panels  mounted  on  angle-iron  framework.  From  the  circuit  diagrams 
heretofore  shown,  the  reader  will  recognize  the  strap-and-disk  arrangement, 
as  well  as  the  spring-jack  and  pin-jack  equipment  mounted  underneath. 

NEW  WESTERN  UNION  SWITCHBOARD  EQUIPMENT 
In  new  construction,  and  in  the  reconstruction  of  switchboard  equipment, 
the  Western  Union  Telegraph  Company  plans  to  make  extensive  use  of  the 


MAIN-LINE  SWITCHBOARDS  FOR  TERMINAL  OFFICES    151 


FIG.  132. — Western  Union  distributing  frame. 


152  AMERICAN  TELEGRAPH  PRACTICE 

pin-jack.  The  aim  is  to  abandon  the  use  of  the  strap-and-disk  equipment, 
also  the  spring- jack  and  wedge  accessories  now  universally  employed  for 
main-line  switching  purposes. 

The  new  type  of  switchboard  consists  of  an  angle-iron  frame,  having 
mounted  on  its  face  porcelain  panels,  each  panel  containing  16  telephone- 
type  pin-jacks,  similar  to  those  previously  illustrated  and  described. 

A  switchboard  containing  ten  panels  will  have  160  pin-jacks,  and  where 
four  jacks  in  series  are  required  to  take  care  of  the  various  operations  of 
" grounding,"  "looping,"  and  " patching,"  a  lo-panel  board  will  accommodate 
40  main-line  wires. 

DISTRIBUTING  FRAMES 

In  new  installations,  the  Western  Union  Company  consolidates  the 
" terminal  room,"  and  "cross-connecting"  frame,  features  as  utilized  in  the 
"Postal"  Company's  service,  forming  a  common  "distributing  frame"  of 
the  type  employed  in  telephone  service. 

Figure  132  shows  a  perspective  view  of  a  section  of  the  distributing  frame, 
which  is  located  near  the  main  switchboard.  All  line  wires  cabled  into  the 
office  from  underground  or  aerial  lines  are  brought  directly  to  the  distributing 
frame  as  also  are  all  cables  from  instrument  tables,  the  various  house  circuits 
being  completed  by  means  of  short  cross-connecting  wires  extending  through 
the  frame.  The  terminal  block  units  for  mounting  on  the  frame  are  made  of 
porcelain,  each  block  having  10  wing-nut  binding  posts. 

The  distributing  frame  as  a  whole  is  made  up  of  "base  units"  and  "top 
units."  The  illustration,  Fig.  132,  is  that  of  a  base  unit. 

Both  sides  of  a  standard  base  unit  will  accommodate  24  terminal  blocks, 
and  both  sides  of  a  standard  top  unit,  the  same  number. 

The  function  of  the  distributing  frame  is  identical  with  that  of  the  cross- 
connecting  frame  previously  described,  that  is,  to  provide  means  for  making 
any  required  connection  between  the  different  sets  of  instruments  in  use,  or 
between  line  wires  and  signaling  instruments  mounted  on  operating  tables, 
without  interfering  with  the  cabled  conductors,  or  disturbing  the  permanent 
wiring  of  the  switchboard  proper. 


CHAPTER  X 
ELECTRICAL  MEASURING  INSTRUMENTS 

TELEGRAPH  LINE  AND  CIRCUIT  TESTING 

The  satisfactory  operation  of  telegraph  circuits  is  almost  entirely  depend- 
ent upon  the  efficiency  of  the  methods  of  testing  practised,  upon  thoroughness 
of  inspection,  and  upon  the  standards  of  line  maintenance  observed  by  the 
operating  department  of  a  telegraph  administration. 

From  the  beginning  of  the  art  and  until  a  comparatively  recent  period, 
the  Tangent  Galvanometer  was  used  almost  exclusively  for  the  purpose  of 
making  tests  and  measurements.  In  recent  years,  however,  the  quickening 
of  the  service  has  created  a  demand  for  more  rapid  methods  of  circuit 
testing,  and  at  the  present  time  the  direct-reading  instruments,  such  as  the 
voltmeter,  ammeter,  and  milammeter,  are  entensively  employed  in  telegraph 
testing.  Even  the  Wheatstone  bridge,  so  long  the  standard  measuring 
instrument,  is  now  used  only  where  accurate  figures  are  necessary. 

The  demands  of  fast  service  are  such  that  modern  practice  recognizes 
the  value  of  qualitative  as  distinguished  from  quantitative  measurements; 
so  much  so  that  we  find  the  simple  telephone  receiver  gaining  favor  as  an 
indicator  of  faults.  True,  the  great  growth  in  the  practice  of  cabling  con- 
ductors has  created  conditions  favorable  to  the  employment  of  the  telephone 
receiver  as  a  fault  finder. 

In  what  follows,  various  practical  and  laboratory  methods  of  making  all 
tests  and  measurements  required  in  practice  are  explained  in  sufficient 
detail  to  enable  the  practical  telegrapher  to  familiarize  himself  with  the 
procedure  customary  in  each  case. 

The  Galvanometer. — The  term  galvanometer  might  correctly  be  applied 
to  any  indicating  instrument  which  measures  the  magnitude  of,  or  indicates 
the  direction  of  electric  currents. 

While  there  are  many  makes  of  galvanometer  in  use,  practically  all  such 
instruments  are  either  of  the  moving-coil  or  moving-needle  type. 

The  former  is  known  as  the  d'Arsonval  type  of  instrument,  in  which  a 
small  coil  of  wire  is  suspended  between  the  poles  of  a  magnet,  with  its  axis 
normally  at  right  angles  to  the  lines  of  force  in  the  magnetic  field. 

The  moving-needle  instrument  has  a  magnetized -steel  needle  or  pointer 
delicately  suspended  with  its  axis  horizontal,  and  having  a  movement  in  a 
horizontal  plane.  Normally  the  indicating  needle  points  in  a  north  and 

153 


154 


AMERICAN  TELEGRAPH  PRACTICE 


FIG.  133. — d'Arsonval  portable  galvanometer. 


FIG.  134. — Mirror  galvanometer. 


ELECTRICAL  MEASURING  INSTRUMENTS  155 

south  direction  due  to  the  influence  of  the  earth's  magnetic  field,  or  to  the 
field  of  artificial  magnets  mounted  near  it.  Close  to  the  center  portion  of 
the  needle,  generally  surrounding  it,  is  mounted  a  coil  of  insulated  wire  with 
its  axis  at  right  angles  to  the  normal  north  and  south  direction  of  the  needle. 
When  the  coil  is  energized  from  a  source  of  electric  current,  the  needle  tends 
to  move  into  a  new  position  to  a  point  somewhere  between  the  original  field 
and  that  of  the  axis  of  the  coil,  the  distance  through  which  the  needle  moves 
being  dependent  upon  the  strength  of  current  in  the  circuit  of  which  the  coil 
winding  forms  a  part. 

The  d'Arsonval  ty'pe  of  instrument  is  the  one  generally  used  for  commer- 
cial measurements. 

So  far  as  the  principles  involved,  and  operation  are  concerned,  the  galva- 
nometer and  the  ammeter  are  identical.  The  former,  however,  may  be  used 
for  detecting  currents  of  a  much  lower  value. 

Figure  133  shows  a  make  of  portable  d'Arsonval  galvanometer  used  in 
connection  with  Wheatstone-bridge  measurements. 

Where  exact  measurements  are  necessary,  a  galvanometer  of  high  sensi- 
bility, such  as  that  illustrated  in  Fig.  134,  is  used.  This  form  of  d'Arsonval 
galvanometer  has  the  moving  element  mounted  between  magnet  poles  and 
suspended  from  a  point  near  the  top  of  an  upright  tube  by  means  of  a  very 
fine  plated  phosphor-bronze,  silver,  or  steel  wire.  A  small  round  mirror  is 
fastened  to  the  moving  element,  reflecting  outward.  The  deflections  of  the 
coil,  resulting  from  the  presence  of  electric  current  in  the  winding,  are  meas- 
ured by  means  of  a  telescope  and  suitable  scale.  The  image  of  the  scale  in 
the  mirror  may  be  read  through  the  telescope,  or  as  variously  used,  the  move- 
ment of  a  spot  of  light  on  a  stationary  scale  mounted  a  short  distance  away 
from  the  mirror  may  be  directly  observed  while  measurements  are  being 
made.  Due  to  the  fact  that  the  moving  coil  and  its  suspension  are  non- 
magnetic, and  that  the  magnetic  field  in  which  the  moving  element  turns 
is  very  strong,  the  readings  of  this  current  indicator  are  not  appreciably 
affected  by  the  earth's  field,  or  other  neighboring  magnetic  disturbances. 

Differential  Galvanometers. — For  comparing  the  relative  strengths  of 
two  currents,  a  galvanometer  is  sometimes  employed  in  which  the  coil  con- 
sists of  two  separate  identical  windings,  mounted  side  by  side.  If  equal 
currents  are  at  the  same  time  sent  through  both  windings,  there  will  be  no 
deflection  of  the  indicating  needle,  but  should  the  currents  be  unequal  in 
strength  the  needle  is  deflected,  due  to  the  influence  of  the  stronger  current; 
to  a  degree  corresponding  to  the  difference  in  the  two  current  strengths. 
When  the  current  strengths  are  equal,  the  effect  of  one  coil  upon  the  needle 
is  completely  neutralized  by  that  of  the  other. 

The  Ballistic  Galvanometer. — Ballistic  galvanometers  are  employed  to 
measure  currents  of  momentary  duration,  such,  for  instance,  as  flow  in  a 
circuit  when  a  condenser  is  discharged  through  it.  With  this  instrument 


156  AMERICAN  TELEGRAPH  PRACTICE 

the  oscillation  period  of  the  needle  must  be  long  as  compared  with  the  dura- 
tion of  each  discharge.  As  the  needle  which  is  long  or  heavy  swings  slowly 
around,  the  amount  of  deflection  is  additive,  that  is,  the  intermittent  indivi- 
dual impulses  impressed  on  the  circuit  result  in  a  cumulative  effect  upon  the 
needle.  Where  no  damping  of  the  needle  is  resorted  to,  the  sine  of  half  the 
angle  of  the  first  swing  is  proportional  to  the  quantity  of  electricity  that  has 
flowed  through  the  coil. 

Galvanometer  Shunts.  —  In  cases  where  it  is  necessary  or  desirable  to  use 
a  high  sensibility  galvanometer  in  making  measurements  requiring  a  con- 
siderably lower  sensibility,  the  galvanometer  coil  may  be  shunted  by  a  resist- 
ance having  a  definite  ratio  to  that  of  the  galvanometer  coil.  A  formula 
for  determining  shunt  values  was  given  on  page  86  in  connection  with 
Fig.  65. 

Where  galvanometers  are  not  equipped  with  regular  shunt-coils  any 
ordinary  resistance  coil  or  coils  of  the  correct  value  may  be  used  for  the  pur- 
pose. As  usually  furnished  with  galvanometers,  shunts  are  adjustable  to 
1/9,  1/99,  or  V999  °f  the  galvanometer  resistance,  so  that  i/io,  i/ioo,  or 
i/iooo  part  of  the  current  only  passes  through  the  galvanometer  coil. 

Constant  of  a  Galvanometer.  —  The  constant  or  sensibility  of  a  galva- 
nometer refers  to  the  value  of  the  resistance  in  ohms  through  which  i  volt 
will  produce  a  deflection  of  one  degree  on  a  standard  scale,  or  to  apply  a 
general  rule: 

Multiply  the  deflection  by  the  multiplying  power  of  the  shunt  and  by  the 
resistance  in  the  standard  resistance  box  expressed  in  megohms  or  fractions 
thereof. 

In  Fig.  135  the  necessary  connections  are  shown  for  taking  the  constant 
of  a  galvanometer. 

R,  is  a  standard  resistance  of  100,000  ohms. 

Closing  the  key  K  will  cause  the  galvano- 
meter to  be  deflected  d  degrees.  If  then  the 
shunt  employed  has  a  multiplying  power  of 
1,000,  obviously  had  no  shunt  been  used  the 
amount  of  deflection  of  the  needle  would 

FIG.  i35.-Taking  the  constant  of   have  been  I'OO°  times  as  8reat      This  at  least 

a  galvanometer.  would    have    been    the    case   theoretically. 

Had    a    resistance  of   1,000,000  ohms  been 

used  in  place  of  100,000,  the  deflection  would  have  been  but  one-tenth  of  d; 
so  that  the  deflection  K,  through  1,000,000  ohms  in  series  with  the  galvano- 
meter coil  with  no  shunt  applied  would  have  been 

i,o 
A  = 


IO 

Where  the  multiplying  power  of  the  shunt  is  represented  by  m,  the  deflection 


ELECTRICAL  MEASUREMENTS 


157 


in  degrees  by  d,  and  the  resistance  in  megohms,  or  fractions  thereof  by  R,  then 

K  =  Rmd. 

The  terms  "constant,"  " figure  of  merit,"  and  "sensibility,"  when  used  with 
reference  to  galvanometers,  have  the  same  meaning. 

MEASURING  THE  RESISTANCE  OF  GALVANOMETERS 

Half -deflection  Method. — Connect  the  galvanometer  as  shown  in  Fig. 
136.  The  resistance  R  and  the  source  of  e.m.f.  B  should  be  so  regulated  that 
the  deflection  of  the  galvanometer  needle  is  over  one-half  of  the  scale. 
Note  the  deflection,  then  increase  the  resistance  R  until  the  needle  moves 


R 

-WAAA- 


FIG.  136.— Half-deflection  method 
of  measuring  the  resistance  of  a  gal- 
vanometer. 


FIG.  137. — Kelvin's   method  of  measur- 
ing the  resistance  of  a  galvanometer 


to  a  point  on  the  scale  exactly  midway  between  zero  and  the  point  of  first 
deflection. 

Disregarding  the  battery  resistance,  the  resistance  of  the  galvanometer 
will  be  the  resistance  of  R  measured  at  "half  deflection,"  less  twice  the 
original  resistance  of  R,  or 

G  =  r-R2. 

Kelvin's  Method. — Connect  the  galvanometer  in  the  X  arm  of  a  Wheat- 
stone  bridge  as  shown  in  Fig.  137  and  adjust  R  until  the  deflection  of  the 
needle  is  the  same  whether  key  K  is  closed  or  open,  then 

:«-*! 

Of  course,  where  two  galvanometers  are  available,  the  instrument  whose 
resistance  is  desired  may  be  inserted  in  the  X  arm,  and  the  " bridge"  balanced 
in  the  usual  manner  by  means  of  the  other  galvanometer. 

THE  VOLTMETER 

Measuring  instruments  which  indicate  the  value  of  the  e.m.f.  in  volts 
impressed  upon  their  terminals  are  called  voltmeters. 

When  a  voltmeter  is  connected  across  the  terminals  of  a  source  of  e.m.f.  a 


158  AMERICAN  TELEGRAPH  PRACTICE 

current  will  flow  through  it  which  is  directly  proportional  to  the  impressed 
voltage.  Attached  to  the  moving  element  (which  in  principle  is  the  same  as 
that  of  the  d'Arsonval  galvanometer)  there  is  a  light  pointer  moving  across 
a  scale  which  has  been  empirically  graduated  into  divisions  to  indicate  the 
value  of  the  impressed  e.m.f.  Contained  within  the  voltmeter  casing  there 
is  a  non-inductive  resistance  ranging  in  ohms  from  10  to  2,000  times  the  full 
scale  reading  in  volts.  This  resistance  is  in  series  with  the  winding  of  the 
movement  coil,  and  it  is  customary  to  insert  100  ohms  or  more  for  each  volt 
as  indicated  on  the  scale.  The  higher  the  series  resistance  per  volt,  the 
greater  will  be  the  accuracy  of  the  indications. 

There  are  various  types  of  voltmeter  available  for  different  needs,  among 
which  might  be  mentioned  the  alternating-current  voltmeter  for  measuring 
currents  of  a  given  frequency,  one  make  of  which  has  a  mass  of  soft  iron 
so  placed  that  it  will  be  moved  into  a  solenoid,  or  from  the  center  of  a 
solenoid  to  one  end,  the  movement  of  the  soft  iron  plunger  controlling  the 
travel  of  a  scale  pointer.  Also  there  are  voltmeters  based  upon  the  principle 
of  the  electrodynamometer  which  may  be  used  for  either  direct-currents  or 
alternating-currents,  and  which  are  independent  of  variations  in  current 
frequency  and  of  wave  form. 

Hot  Wire  Meters. — Hot-wire  voltmeters  and  ammeters  are  used  in 
which  the  passage  of  current  through  a  length  of  thin  wire  causes  a  rise  of 
temperature  with  consequent  expansion  of  the  metal  conductor.  As  the 
wire  expands,  the  slack  is  taken  up  by  a  spring,  the  resulting  movement  of 
which  causes  a  pointer  to  travel  across  a  properly  graduated  scale,  thus 
indicating  the  strength  of  the  current  traversing  the  hot  wire. 

MULTIPLIERS  FOR  VOLTMETERS 

The  range  of  a  given  voltmeter  may  be  increased  by  employing  a  suitable 
multiplier  in  the  form  of  an  additional  external  resistance  placed  in  series 
with  the  voltmeter.  With  a  low-reading  voltmeter  and  a  set  of  multipliers 
it  is  practicable  to  measure  voltages  covering  a  large  range  of  values.  As- 
sume, for  instance,  that  the  only  meter  available  is  a  5o-volt  instrument, 
having  5,000  ohms  resistance,  and  that  it  is  desired  to  use  the  meter  for 
measuring  higher  voltages.  A  multiplier  with  a  value  of  2  would  measure 
10,000  ohms,  which  would  give  a  scale  value  for  the  meter  of  100  volts.  A 
multiplier  with  a  value  of  10  used  with  the  50- volt  meter  would  measure 
50,000  ohms,  which  would  give  the  meter  a  scale  value  of  500  volts.  It  is, 
of  course,  understood  that  50,000  ohms  would  represent  the  total  resistance 
of  meter  and  multiplier  in  series. 

A  formula  applicable  to  any  requirement  might  be  stated  thus: 


ELECTRICAL  MEASURING  INSTRUMENTS  159 

where  R  is  the  resistance  of  the  voltmeter,  Rr  the  multiplier  resistance  to  be 
connected  in  series  with  the  meter,  V  the  highest  reading  of  the  meter  nor- 
mally, and  V  the  highest  reading  desired. 

V 

The  scale  reading  observed  must  be  multiplied  by  -~  to  obtain  the  correct 

value  of  the  e.m.f. 


CURRENT  METERS 

The  ammeter  and  the  milliammeter  are  instruments  for  measuring  the 
current  strength  in  circuits,  the  indicating  scales  being  marked  off  into  divi- 
sions representing  amperes  and  milliamperes  respectively.  In  the  series 
ammeter  the  entire  current  to  be  measured  traverses  the  coil  winding  of  the 
instrument,  and  as  in  the  case  of  the  galvanometer,  variations  in  the  current 
strength  cause  the  indicating  needle  to  be  deflected  to  a  greater  or  less  degree 
from  its  position  of  rest,  the  amount  of  deflection  being  dependent  upon  the 
value  of  the  current  in  the  circuit.  For  currents  of  any  considerable  volume, 
the  shunt  ammeter  is  generally  employed  in  which  a  small  portion  only  of 
the  current  is  carried  by  the  instrument  coil.  In  portable  ammeters  the  shunt 
coil  is  mounted  in  the  base  of  the  instrument. 


BATTERIES  FOR  TESTING  PURPOSES 

Where  line  tests  are  made  from  terminal  or  intermediate  test  offices, 
generally  there  is  available  current  from  motor-generators  or  gravity  bat- 
teries which  may  be  applied  in  any  desired  manner,  but  where  measurements 
are  to  be  made  from  manholes  giving  access  to  underground  cables,  from  aerial 
cable  boxes,  or  from  any  point  where  regular  battery  is  not  available,  it  is 
necessary  to  employ  a  portable  battery  for  the  purpose. 

Modern  Wheatstone  bridge  sets  have  a  self-contained  dry  battery  source 
of  e.m.f.  which  yields  a  current  of  sufficient  strength  for  making  all  ordinary 
"bridge"  measurements.  They  are  also  equipped  with  a  conveniently 
mounted  battery  switch  which  makes  possible  regular  main-line  switch- 
board battery  connections  when  the  bridge  is  used  for  line  testing  from  a 
terminal  office. 

Where  the  resistances  involved  are  not  great,  ordinarily,  dry  cells  serve 
the  purpose  satisfactorily,  but  in  cases  where  high  resistances  are  to  be  dealt 
with  in  making  certain  tests,  potentials  of  at  least  50  or  100  volts  are  best 
suited  to  the  purpose. 

Formerly  the  chloride  of  silver  battery  was  extensively  used  for  testing 
purposes.  This  form  of  battery  met  the  requirements  admirably,  and  has 
only  recently  given  way  to  the  more  efficient  storage  battery,  which  is  now 
available  in  light  and  compact  units. 


160  AMERICAN  TELEGRAPH  PRACTICE 

One  excellent  make  of  portable  storage  battery  designed  for  testing  pur- 
poses is  known  as  the  "Witham,"  or  Marcuson  battery.  Several  small 
storage  cells  are  assembled  in  boxes  to  form  batteries  having  certain  ranges  of 
voltage.  There  are  four  standard  sizes,  having  maximum  voltages  as  follows : 
100  volts,  140  volts,  1 68  volts,  and  256  volts.  The  boxes  containing  the 
battery  complete  weigh  17  1/2,  24  1/2,  29,  and  42  Ib.  respectively.  These 
batteries  are  divided  into  two  or  more  sections,  which  by  means  of  a  commu- 
tating  switch  may  be  connected  in  series  or  in  parallel,  thus  giving  at  the 
terminals  either  the  full  voltage  of  the  battery  or  a  fraction  of  same. 

THE  WHEATSTONE  BRIDGE 

This  instrument  consists  of  an  arrangement  of  conductors  as  shown 
theoretically  in  Fig.  138.  One  terminal  of  the  battery  is  led  to  the  point 
d,  where  it  divides  into  two  paths  which  are  united  again  at  the  point  c,  so 
that  a  portion  of  the  total  current  flowing  passes  through  the  point  e, 

and  a  portion  through  the  point  /.     The 
four   conductors  a,   b,  R,   and  X    are 
called  the  "  arms  "  of  the  bridge.     When 
the  electrical  resistances  of  three  of  the 
arms  are  known,  the  resistance  of  the 
fourth  may  be  calculated  according  to 
the  proportions  of  their  relative  values. 
What  was   said  on  page  87  in  re- 
FIG.  i38.-Theoretical  connections  of  the  gard  to  «  f dl  of  potential  along  a  con- 
ductor"  (Fig.  66)  has  a  direct  bearing 
upon  the  underlying  principle  of  the  Wheatstone  bridge. 

Referring  to  Fig.  138:  It  is  obvious  that  there  will  be  a  fall  of  electric 
potential  between  the  battery  terminal  and  the  point  d;  also  that  there  is  a 
further  drop  along  the  upper  branch  d,f,  c,  and  that  the  potential  of  the  lower 
branch  falls  along  the  path  d,  e,  c.  If  the  point  e  and  the  point/  are  equally 
distant,  electrically,  from  the  point  d,  and  in  the  same  sense  equally  distant 
from  the  point  c,  then  the  potential  will  have  fallen  at  e  to  the  same  value  it 
has  fallen  to  at  the  point/,  or  if  the  ratio  of  the  resistance  a  to  the  resistance  R 
be  equal  to  the  existing  ratio  between  b  and  X,  then  the  points  e  and  f  will  have 
equal  potentials.  Connecting  a  galvanometer  between  the  points  e  and/,  as 
shown,  furnishes  a  means  whereby  it  is  possible  to  observe  whether  or  not  the 
points  e  and/  are  at  equal  potentials.  When  such  is  the  case,  there  will  be  no 
deflection  of  the  galvanometer  needle,  or  when  the  resistances  of  the  four  arms 
are  in  "balance"  we  have  by  proportion 

a:b:  :R:X, 
and  if  we  know  the  resistance  values  of  a,  b,  and  R}  X  may  be  determined  thus: 


THE  WHEATSTONE  BRIDGE  161 

The  unknown  resistance  or  the  resistance  to  be  measured  is  inserted  at  X,  that 
is,  between  the  points  d  and  e. 

When  the  resistance  to  be  measured  is  not  greater  than  the  total  resistance 
of  R,  the  ratio  arms  a  and  b  may  be  made  equal,  then  if  the  rheostat  arm  (R) 
of  the  bridge  be  adjusted  until  the  galvanometer  indicates  a  "balance,"  it  is 
plain  that  the  unknown  resistance  (X)  has  a  value  equal  to  that  of  R. 

When  it  is  desired  to  measure  a  resistance  greater  than  the  total  value  of 
R,  the  ratio  arm  b  should  be  given  a  higher  value  than  a,  and  to  measure  very 
low  resistances  the  ratio  arm  b  should  be  given  a  value  less  than  that  of  a. 

For  example,  let  a  =  10  b      i  ooo 

5  =  i,ooo  khen-X'  =  -  =  —   —  X54o  =  54,ooo.    :> 


then  X  = X  540  =  5.4. 


Let  a  =  1,000 


=  io 


COMMERCIAL  WHEATSTONE  BRIDGE  INSTRUMENTS 

There  are  several  large  instrument  houses  that  manufacture  high-grade 
measuring  instruments  and  bridge  sets,  and  when  such  apparatus  is  given 
proper  care  after  being  delivered  by  the  manufacturer,  generally  it  will  be 
found  to  be  quite  constant  and  reliable  in  performance,  and  will  have  long  life. 

One  of  the  newer  makes  of  bridge  is  illustrated  in  Fig.  139.  In  this 
particular  set  the  battery  is  inclosed  within  the  casing  and  consists  of  four 
dry  cells  of  a  stock  size.  The  rheostat,  or  R  arm  of  the  bridge  system  is 
composed  of  four  dials  of  ten  coils  each,  which  have  values  of  units,  tens, 
hundreds  and  thousands  ohm  coils.  The  ratio  arms  a  and  b  have  values  of 
i,  10,  100  and  1,000  ohms  in  each  arm.  The  galvanometer,  which  is  of  the 
d'Arsonval  type,  is  mounted  flush  with  the  floor  of  the  box  containing  the 
resistance  coils.  The  scale  has  30  millimeter  divisions  with  center  zero. 
A  zero  adjustment  is  provided  which  enables  the  tester  to  bring  the  needle 
exactly  on  zero,  or  on  any  point  of  the  scale  desired.  Instead  of  metallic 
plugs  being  used  to  cut-in  or  cut-out  the  various  resistance  units,  radial 
brush  contacts  are  provided  which  swing  in  a  complete  circle  in  either 
direction,  going  from  the  highest  value  to  the  lowest  value  coil  in  any  decade, 
without  having  to  be  turned  back  over  the  intervening  contacts. 

By  means  of  extra  binding-posts  and  accessible  switches  it  is  possible  to 
substitute  an  external  source  of  e.m.f.  in  place  of  the  dry-cell  battery  con- 
tained within  the  box,  and  to  employ  a  separate  galvanometer  in  place  of 
the  one  mounted  as  a  part  of  the  set. 

Included  as  a  part  of  the  equipment  of  the  set  is  an  Ayrton  shunt 
which  allows  full  current,  i/io  part,  or  i/ioo  part  of  the  current  to 
11 


162  AMERICAN  TELEGRAPH  PRACTICE 

flow  through  the  galvanometer  of  the  set  or  external  galvanometer,  which- 
ever is  used  with  the  bridge  at  the  time. 

The  set  described,  in  common  with  other  modern  Wheatstone  bridge  sets, 
may  be  used  in  making  the  following  tests: 


THOMPSON    teVEff/NGCO  PHILA.PA 

._ 


FIG.  139. — Commercial  form  of  wheatstone  bridge,  including  galvanometer  and  self- 
contained  dry-cell  battery. 

Measuring  resistance  by  the  bridge  method. 

Measuring  insulation  resistance  by  the  direct  deflection  method. 

Comparing  e.m.f.'s  by  the  fall  of  potential  method. 

Checking  up  voltmeters. 

Measuring  battery  resistance. 

Making  the  Murray  loop  test. 

Checking  up  ammeters  by  using  a  shunt  of  known  value. 

Making  the  Varley  loop  test. 

Testing  out  "grounds." 

The  galvanometer  and  battery  can  be  used  in  series. 

THE  ELECTRIC  CONDENSER 

The  fact  that  both  long  and  short  metallic  conductors  used  in  form- 
ing electrical  circuits  possess  capacity,  means  that  when  the  electrostatic 
capacity  of  a  conductor  is  to  be  measured,  or  when  the  static  discharge 
from  line  conductors  is  to  be  compensated  for,  it  is  sometimes  necessary 


THE  ELECTRIC  CONDENSER 


163 


to  have  available  for  these  purposes  electric  condensers  having  variable 
capacities. 

In  considering  the  theory  of  the  electric  condenser,  it  might  be  stated 
that  the  factors  involved  are  a  source  of  electric  charge,  a  conductor  of 
electricity,  and  a  dielectric  (insulator). 

One  of  the  most  comprehensive  generalizations  relating  to  electro- 
statics, established  by  Faraday,  was  that  all  electric  charge  and  discharge 
is  essentially  the  charge  and  discharge  of  a  Leyden  jar  (a  form  of  electric 
condenser). 

The  original  form  of  condenser,  the  Leyden  jar,  owes  its  name  to  the 
city  in  which  it  was  invented.     The  appearance  of  this 
condenser  is  illustrated  in  Fig.  140. 

Later  forms  of  the  Leyden  jar  were  made  with  an 
inside  and  an  outside  coating  of  tin-foil  reaching  from 
the  bottom  to  within  2  or  3  in.  of  the  top  of  the 
glass  jar.  A  shellaced  wooden  top  fitted  into  the 
neck  of  the  jar,  served  as  a  support  for  a  brass  knob 
mounted  on  the  upper  end  of  a  brass  wire;  the  latter 
extending  through  a  hole  in  the  top  had  affixed  to  its 
lower  or  inside  end  a  length  of  brass  chain  reaching 
to  the  bottom  of  the  jar  and  in  contact  with  the  in- 
side foil  coating:  the  efficiency  of  the  jar  as  a  con- 
denser being  considerably  increased  by  the  applica- 
tion of  a  coating  of  shellac,  due  to  the  fact  that  shellac 


very  materially  retards  the  dissipation  of  the  charge 


***•  T4°  -Original  form 
.        of  Leyden-jar  condenser. 
over  the  uncovered  surfaces  of  the  jar.     Condensation 

of  moisture  on  the  surface  of  the  glass  interposes  a  conducting  path,  even  if 
of  very  high  resistance,  which  permits  gradual  equalization  of  the  opposite 
charges  gathered  on  the  tin-foil  surfaces  attached  to  the  inside  and  to  the 
outside  of  the  jar. 

From  this  brief  description  it  is  evident  that  a  Leyden  jar  condenser, 
like  any  other  form  of  electric  condenser,  consists  simply  of  two  conductors 
separated  by  an  insulator.  The  capacity  of  any  form  of  condenser,  that  is, 
its  ability  to  retain  a  greater  or  less  quantity  of  charge,  is  dependent  upon 
the  area  of  the  conducting  surfaces  and  upon  their  distance  apart. 


COMMERCIAL,  OR  STANDARD  CONDENSERS 

The  capacity  of  commercial  condensers  is  either  fixed  or  variable,  or 
as  more  commonly  stated,  non-adjustable  or  adjustable,  respectively. 

A  non-adjustable  condenser  has  its  conducting  surfaces,  or  leaves, 
arranged  as  shown  in  Fig.  141,  in  which  the  leaves  are  represented  by  vertical 
lines  and  the  connecting  metal  strips  by  horizontal  lines. 


164  AMERICAN  TELEGRAPH  PRACTICE 

Alternate  leaves  are  connected  with  the  metal  strip  A,  while  every 
other  alternate  leaf  is  connected  with  the  metal  strip  B,  as  shown.  Conden- 
sers constructed  so  that  their  capacity  may  be  adjusted  or  varied,  have 
alternate  leaves  connected  with  a  common  terminal  as  shown  in  Fig.  142, 
while  the  remaining  alternate  leaves  are  connected  in  groups  which  may  be 
placed  in  contact  with  the  other  condenser  terminal  B,  at  i,  2,  3,  4,  etc., 
as  desired,  by  inserting  metallic  plugs  in  contact  plates  distributed  at  these 
points. 

It  is  important  to  note  that  an  adjustable  condenser  when  completely 
assembled  and  connected  for  full  capacity,  is  simply  a  number  of  non- 
adjustable  condenser  units  arranged  in  parallel. 


I  LU  iiu  i  in  iiu  i  ui 


12345 
B 


FIG.  141.  FIG.  142. 

Capacity  of  Condensers.  —  The  joint  capacity  of  condensers  connected  in 
parallel  is  equal  to  the  sum  of  their  respective  capacities,  or  in  the  case  of 
two  condensers 

Total  capacity  =  Ci+C2 

The  joint  capacity  of  two  condensers  connected  in  series  is  equal  to  the  prod- 
uct divided  by  the  sum  of  their  respective  capacities,  or 

c  xc 

Total  capacity  =  >r 


Where  three  condensers  are  connected  in  series,  the  joint  capacity 


— -4-— +— 
r  ~" '  r   '  r1 

**'i        <-/2        ^3 

Or  for  any  number  of  condensers  in  series,  the  joint  capacity  is  equal  to  the 
reciprocal  of  the  sum  of  the  reciprocals  of  their  respective  capacities,  thus 
following  the  law  of  the  joint  resistance  of  parallel  circuits  as  explained  in  a 
previous  chapter.  When  combined  in  multiple  series,  the  same  law  applies, 
the  total  capacity  of  each  group  of  condensers  connected  in  parallel  being 
regarded  as  the  capacity  of  a  single  condenser  in  order  to  obtain  values  for  the 
purpose  of  computing  the  total  capacity  available  from  a  given  arrangement. 

MEASURING  CAPACITY 

Occasionally  it  is  necessary  to  determine  the  capacity  of  a  condenser, 
a  line  wire,  or  cable  conductor.     One  method  of  obtaining  the  desired  in- 


MEASURING  "CAPACITY" 


165 


formation  is  that  known  as  the  direct  deflection  method,  and  the  procedure 

is  as  follows:  charge  a  standard  condenser  Ci  Fig.  143,  from  a  source  of 

e.m.f.  for  a  period  of,  say,  30  seconds,  then  discharge  the  condenser  through  a 

galvanometer  (preferably  a  ballistic,  or  an  astatic  galvanometer);  note  the 

deflection  and  call  it  d.    Next  charge  the 

condenser  to    be    measured  from   the 

same  battery  and  for  the  same  period 

of  time,  and  discharge  it  through  the 

galvanometer    in    the    same   manner. 

Note  the  deflection  of  the  needle,  and 

call  this  di 


Then 
and 


CuCiidid 


di 
ld' 


C, 


K 


II- 


FIG.  143. — Measuring  the  capacity  of  a 
condenser  by  the  direct-deflection  method. 


Bridge  Method. — Connect  the  two  condensers  to  be  compared  as  shown 
in  Fig.  144.  Ri  and  R%  are  non-inductive  resistances  of  about  2,000  ohms 
each,  G  a  galvanometer,  E  a  source  of  e.m.f.,  and  K  a  key.  Adjust  the 
resistances  Ri  and  R2  so  that  there  is  no  deflection  of  the  galvanometer 
needle  when  the  key  K  is  manipulated. 


Then 


~\  •                         *t 

(\\(i. 

K 

™     E 

mm 

mm 

c, 

FIG.  144. — Comparing  the  capacity  of  condensers  by  the  bridge  method. 

Modern  commercial  adjustable  condensers  are  made  up  of  a  number  of 
small  units  assembled  within  a  sheet-iron  or  tin  case,  equipped  with  sliding 
contacts  controlled  by  a  revolving  knob  by  means  of  which  the  capacity  of  the 
condenser  is  varied.  The  sliding  contacts  take  the  place  of  the  peg-and-hole 
connections  formerly  used. 

Insulation  Resistance  of  Condensers. — It  might  be  supposed  that  the 
insulation  resistance  between  the  two  terminals  of  a  condenser  is  infinitely 
high,  but  it  is  found  that  condensers,  as  usually  manufactured,  sometimes 
have  an  insulation  resistance  so  low  that  when  the  condenser  is  inserted 


166 


AMERICAN  TELEGRAPH  PRACTICE 


between  line  and  ground,  the  circuit  through  the  condenser  in  reality 
forms  a  high-resistance  leak.  In  telegraph  practice,  a  condenser  which  is 
found  to  have  an  insulation  resistance  between  terminals  of  not  less  than 
500,000  ohms  is  regarded  as  satisfactory  for  all  practical  requirements. 
Using  a  standard  milammeter,  with  an  applied  e.m.f.  of  375  volts,  one 
division1  deflection  on  the  lower  scale  of  the  milammeter  represents  an  in- 
sulation of  1.8  megohms.  Therefore  a  condenser  tested  with  375  volts 
pressure  which  shows  more  than  3  1/2  divisions  deflection  on  the  lower 
scale  of  the  milammeter  has  an  insulation  resistance  too  low  for  satisfactory 
service. 

MEASURING  THE  INTERNAL  RESISTANCE  OF  BATTERIES 

The  well-known  half-deflection  and  direct-deflection  methods  of  measur- 
ing  the  internal   resistance   of  batteries,   formerly  extensively  employed, 


V.M. 


4-  B 


A.M. 


FIG.  145. — Measuring  the  internal  re- 
sistance of  a  battery  by  the  voltmeter- 
ammeter  method. 


FIG.  146. — Measuring  the  internal  re- 
sistance of  a  battery  by  the  bridge  method. 


have  been  superseded  in  modern  practice  by  the  employment  of  the  volt- 
meter-ammeter, and  the  bridge  methods  of  making  these  measurements. 

Voltmeter-ammeter  Method.  —  In  making  this  test  the  ammeter  is  con- 
nected through  a  resistance  in  series  with  the  battery,  the  internal  resistance 
of  which  is  sought,  while  a  high-resistance  voltmeter  is  connected  in  shunt 
with  the  ammeter  circuit  as  shown  in  Fig.  145. 

With  the  key  K  open,  the  volmeter  reading  E  is  noted.  Then  with  the 
key  closed  simultaneous  readings  may  be  taken  of  the  voltmeter  E\  and  the 
ammeter  7,  then  the  resistance  of  the  battery 


Bridge  Method.  —  The  battery  to  be  measured  is  connected  in  the  X  arm 
of  the  bridge  as  shown  in  Fig.  146.  With  a  and  b  equal,  adjust  R  until  the 
galvanometer  deflection  with  the  key  K  open  or  closed  is  the  same. 

1  Five  divisions  on  the  lower  scale  represent  i  milampere. 


EARTH  CURRENTS  167 

On  account  of  the  necessity  for  altering  the  regular  bridge  set  connections 
when  making  this  test,  it  is  generally  preferable  to  employ  a  portable  gal- 
vanometer and  separate  resistance  boxes. 

EARTH  CURRENTS 

In  those  measurements  where  the  ground  is  used  as  a  portion  of  the 
completed  circuit,  occasionally  earth  currents  introduce  errors  which  make 
the  readings  unreliable.  Also  it  is  of  considerable  importance  in 
certain  operations  to  determine  the  value  of  the  difference  of  potential 
between  terminal  offices  due  to  earth  currents.  In  the  case  of  grounded- 
circuit  measurements,  where  the  earth  current  is  fairly  constant  in  potential 
and  polarity,  its  effect  may  be  compensated  for  by  making  first  a  measure- 
ment with  the  negative  pole  of  the  home  battery  to  line,  and  then  with  the 
positive  pole  to  line.  If  the  readings  have  an  appreciable  difference  in  value, 
their  average  should  be  taken  as  the  correct  result. 

Measuring  Earth  Potentials. — There  are  several  methods  of  determining 
the  potential  of  the  earth  between  two  points,  but  for  practical  requirements 
the  simplest  way,  and  which  requires  no  calculation,  is  to  use  a  voltmeter  for 
the  purpose.  If  the  meter  has  a  double  scale,  use  the  one  giving  the  greatest 
deflection  with  minimum  potential  difference. 

To  make  the  test,  remove  all  regular  battery  from  the  line.  Ground  the 
line  at  both  ends,  that  is,  at  each  terminal  of  the  wire  under  test.  Connect 
the  voltmeter  into  the  line  at  the  switchboard  by  means  of  a  "wedge"  or 
otherwise.  This  will  connect  the  voltmeter  direct  from  line  to  ground.  If 
when  the  meter  circuit  is  closed  while  the  binding-post  marked  (+ )  is  to  line, 
the  indicating  needle  moves  to  the  right,  then  the  ground  at  the  distant  sta- 
tion is  positive  to  the  home  ground.  If  the  needle  swings  to  the  left,  reverse 
the  wedge  so  that  the  post  marked  (+)  connects  with  the  home-station  ground 
in  which  case  the  ground  at  the  distant  station  is  negative  to  the  home 
ground.  In  noting  the  readings,  the  polarity  as  well  as  maximum  and  mini- 
mum potential  readings  should  be  recorded. 

MEASURING  THE  RESISTANCE  OF  EARTH  CONNECTIONS 

One  method  of  ascertaining  the  value  of  the  earth  resistance  between  two 
stations  which  may  be  applied  where  two  line  wires  are  available  between  the 
stations,  is  shown  in  Figs.  147  and  148.  ' 

The  two  line  wires  are  "looped"  together  at  the  distant  station,  and  at  the 
home  station  are  connected  in  the  X  arm  of  the  bridge,  as  illustrated  in  Fig. 
147.  The  looped  resistance  is  noted.  Assume,  for  example,  that  it  is  found 
to  be  6,000  ohms.  Call  this  RI.  Then,  as  in  Fig.  148,  measure  the  resistance 
of  one  of  the  wires  between  the  home  station  and  the  ground  at  the  distant 


168 


AMERICAN  TELEGRAPH  PRACTICE 


station.  In  like  manner  measure  the  resistance  of  the  other  wire.  Say 
that  one  was  found  to  measure  3,204  ohms,  and  the  other  2,812  ohms,  or 
a  total  of  6,01 6  ohms.  Call  this  value  R2.  Then,  resistance  of  the  distant 
ground  (assuming  that  the  resistance  of  the  home  ground  is  nil) 


or 


6,016  —  6,000-7-2 


Ans.  8  ohms. 


FIG.  147. 


FIG.  148. 
FIGS.  147  AND  148. — Measuring  the  resistance  of  earth  contacts. 

In  view  of  the  variable  conductivity  of  contacts  made  through  "peg" 
switchboards,  where  this  method  of  grounding  is  employed,  it  is  essential 
that  positive  contacts  be  made,  otherwise  errors  will  be  introduced  which 
produce  misleading  results.  It  is,  however,  an  excellent  and  quick  method 
of  determining  whether  or  not  a  suspected  ground  connection  has  a  resistance 
abnormally  high. 

Another  method,  and  one  which  takes  into  consideration  the  value  of 
the  voltage  impressed  on  line  wires  due  to  earth  potentials,  is  shown  theo- 
retically in  Fig.  149. 

In  this  test,  the  regular  galvanometer  of  the  bridge  set  is  replaced  with  a 
voltmeter,  all  other  connections  remaining  the  same.  The  resistance  of 
the  line  wire  extending  between  the  home  station  and  the  station  where  the 
ground  resistance  is  to  be  determined  is  measured  by  means  of  the  loop 
method,  after  which  this  wire  is  "grounded"  at  the  distant  station.  The 
R  arm  of  the  bridge  has  all  of  its  resistance  plugged  out,  then  with  the  arm 


MISCELLANEOUS  TESTS  169 

a  or  b  opened  temporarily  the  voltmeter  indicates  the  value  of  the  earth  poten- 
tial from  the  distant  ground.  In  most  cases  this  value  will  be  found  to  fluc- 
tuate somewhat,  and  it  will  be  necessary  in  such  cases  to  note  the  mean  deflec- 
tion. The  key  should  be  left  open  while  this  reading  is  taken.  Now  close 
the  key  and  with  positive  pole  of  battery  to  line  raise  the  resistance  of  the  R 
arm  of  the  bridge  until  the  deflection  is  of  the  same  value  as  that  first  observed. 
Call  this  reading  A.  Reverse  the  battery  terminals  so  that  the  negative 
pole  will  be  to  line.  Close  the  key  and  adjust  the  resistance  R  until  the  volt- 
meter again  shows  the  same  value.  Call  this  reading  of  R,  B. 


FIG.  149. — Measuring  the  resistance  of  earth  contacts,  where  earth  currents  exist. 

Then  the  resistance  of  the  line  wire  plus  that  of  the  ground  connections 
at  each  end  will  be 

AXB 
A  +  B  2' 

If  the  line  resistance  as  at  first  calculated  is  now  deducted  from  the  result 
obtained,  the  remaining  figure  will  represent  the  resistance  of  the'  distant 
ground  connection.  Assuming,  of  course,  that  the  resistance  of  the  home 
ground  connection  is  known  to  be  nil. 

MISCELLANEOUS  TESTS 

In  what  follows,  various  methods  of  testing  " opens,"  "grounds," 
"crosses,"  "escapes,"  "insulation,"  "conductivity,"  "resistance,"  "capac- 
ity," etc.,  will  be  explained.  It  might  be  deemed  sufficient  to  give  one  ap- 
proved method  of  making  each  measurement  or  test,  but  as  it  is  not  likely 
that  the  testing  equipment  of  a  given  telegraph  administration,  or  of  a  given 
railroad  telegraph  system  is  the  same  at  all  of  its  testing  offices,  it  has  been 
thought  best  to  submit  alternative  methods  covering  each  test,  so  that  no 
matter  what  the  conditions  are  the  attendant  may  have  at  hand  a  method 
of  making  the  desired  test  which  will  meet  the  requirements. 

It  is  well,  too,  for  the  younger  wire  chiefs  to  seek  an  understand  ing  of  the 
various  standard  methods  of  making  all  necessary  measurements,  for,  by 
virtue  of  possessing  such  knowledge  they  are  better  able  to  grasp  the  principles 
involved  and  to  understand  the  subject  generally. 


170 


AMERICAN  TELEGRAPH  PRACTICE 
WHEATSTONE  BRIDGE  MEASUREMENTS 


Where  strap-and-disk  main-line  switchboards  are  employed,  the  practice 
of  the  Postal  Telegraph- Cable  Company  provides  permanent  connections 
between  the  testing  set  and  disks  in  the  main-line  board,  as  shown  in  Fig.  150. 


Main  5wifth board 


FIG.  150. — Wheatstone  bridge  permanently  connected  to  main  line  switchboard. 

It  may  be  seen  that  the  line  binding-posts  (the  X  arm)  of  the  bridge  are 
connected  to  separate  disks  in  the  switchboard,  and  that  a  third  wire  is 
brought'  to  another  disk  in  the  switchboard  for  the  purpose  of  grounding 

one  side  of  the  bridge  when 
so  required  in  making  certain 
tests.  The  electrical  connec- 
tions of  the  bridge  shown 
are  identical  with  those 
shown  in  the  theoretical 
bridge  diagram,  Fig.  138, 
with  the  exception  that 
short-circuiting  switches  are 
provided  for  the  purpose  of 
permanently  closing  the  gal- 
FIG.  151.— Theoretical  circuits  of  bridge  connected  to  vanometer  and  battery  keys, 
main  line  switchboard.  Also,  a  battery  .  reversing 

switch  and  a  grounding  switch 

are  added  for  convenience  in  making  required  tests.  Theoretically  the  con- 
nections would  be  as  shown  in  Fig.  151. 

Practically  all  of  the  troubles  to  which  telegraph  lines  are  subject  may  be 
investigated  with  the  bridge  circuits  arranged  as  shown  in  Fig.  152. 


THE  MURRAY  LOOP  TEST 


171 


In  those  cases  where  the  resistance  of  a  " cross"  varies  within  wide  limits, 
and  a  third  wire  is  taken  for  the  purpose  of  making  the  desired  measurement, 
the  battery  is  "grounded"  as  shown  in  Fig.  153,  the  other  bridge  connections 
remaining  the  same. 


FIG.  152. — Arrangement  of  bridge  connections  for  locating  faults  in  telegraph 

circuits. 

Wheatstone  bridge  measurements  are  divided  into  two  general  classes, 
usually  spoken  of  as  the  "Murray"  and  the  "Varley"  methods.  In  making 
certain  tests,  the  Murray  method  offers  an  excellent  means  of  obtaining  quick 
results.  In  other  cases  this  method  of  testing  is  not  as  applicable,  owing  to 


FIG.  153, 

the  requirement  that  the  conductors  under  test  must  be  of  the  same  size  and 
length,  and  of  the  same  material.  The  Varley  method  is,  generally  speaking, 
more  applicable  to  everyday  telegraph  requirements  than  is  the  Murray 
method. 


THE  MURRAY  LOOP  TEST 

Referring  to  Fig.  154.  Where  it  is  desired  to  locate  grounds  or  crosses  in 
open  lines  or  in  cables,  when  the  Murray  method  is  employed  it  is  not  neces- 
sary that  the  ohmic  resistance  of  the  conductors  under  test  be  known,  so  long 
as  both  wires  comprising  the  loop  formed  are  of  the  same  length,  size,  and 
kind. 

For  the  purposes  of  telegraph  line  testing,  generally  1,000  ohms  is  the 


172 


AMERICAN  TELEGRAPH  PRACTICE 


best  resistance  to  have  cut-in  in  the  a  arm  of  the  bridge.  As  shown  in  Fig. 
154,  the  arm  b  is  short  circuited;  the  adjustable  resistance  (arm  R)  now  in 
effect  taking  the  place  of  the  arm  b.  The  testing  battery  is  connected  to  the 
dividing  point  D,  through  the  key  BK;  the  galvanometer  and  its  key  GK,  to 
the  bridge  terminals  GW  and  FW. 


Good  Wire 


I 


FW 


Fault 


T 

FIG.  154. — Bridge  circuits  arranged  for  locating  a  "ground"  by  the  Murray  loop  test. 

TO  LOCATE  A  GROUND 

Loop  the  faulty  wire  with  a  good  conductor  of  the  same  gage  and  length  at 
the  distant  station.  Connect  the  good  wire  to  the  terminal  GW,  and  the 
faulty  wire  to  the  terminal  FW.  Obtain  a  "balance"  by  closing  both  bat- 
tery and  galvanometer  keys  for  a  moment,  repeatedly.  At  the  same  time 
adjust  the  resistance  of  the  rheostat  until  there  is  no  response  of  the  galva- 
nometer needle  to  the  manipulation  of  the  keys.  Then,  the  distance  to  the 
fault  may  be  determined  by  applying  the  following  formula: 

RXL 


x= 


B+R 


FW 


Fault 
FIG.  155. — Bridge  circuits  arranged  for  locating  a  "cross"  by  the  Murray  loop  test. 

Where  X  represents  " distance"  to  fault. 

B  represents  resistance  in  a  arm  of  bridge. 

R  represents  resistance  in  rheostat  after  balancing. 

L  represents  length  of  loop  in  feet  or  miles. 

To  illustrate:  Suppose  the  conductor  under  test  is  3,700  ft.  in  length,  then  the 


VARLEY  LOOP  TESTS  173 

length  of  the  loop  formed  by  two  similar  lengths  would  be  7,400  ft.  If  when  a 
balance  has  been  obtained  it  is  found  that  the  unplugged  resistance  in  the 
rheostat  is  42  ohms,  and  1,000  ohms  resistance  in  arm  a,  then  the  distance  from 
the  testing  station  to  the  fault  is : 

7400x42 = 310800        ft 

1000+42       1042 

CROSSES 

Should  the  fault  be  a  cross  instead  of  a  ground,  ground  one  of  the  crossed 
wires  as  shown  in  Fig.  155. 

CORRECTION  FOR  LEAD -WIRE  RESISTANCE 

It  is  well  to  avoid  the  employment  of  connecting  wires  between  the 
bridge  and  the  conductors  under  test.  When  necessary  to  do  so,  use  wires 
of  the  same  gage,  or  of  the  same  aggregate  dimension  as  the  conductors,  and 
add  the  combined  length  of  the  connecting  wires  to  the  length  of  the  loop 
formed  by  the  conductors  proper.  After  obtaining  the  result  by  the 
formula  given,  deduct  the  length  of  the  short  wire  connected  to  the  faulty 
conductor,  and  the  remainder  will  be  the  distance  to  the  fault.  For  in- 
stance, if  in  the  previous  example,  it  were  necessary  to  use  connecting  wires 
10  ft.  in  length,  the  formula  would  resolve  into: 

(7400  +  io  +  io)X42     7420X42    3 1 1640  _ 

—  200. 
1000+42  1042  1042 

299-10  (length  of  one  connecting  wire)  =  289  ft.,  distance  to  fault. 
VARLEY  LOOP  METHOD 

In  those  instances  where  faults  are  to  be  located  on  loops  formed  of 
conductors  having  sections  of  different  dimensions,  the  Varley  method  may 
be  used  to  good  advantage. 


FIG.  156. — Bridge  circuits  arranged  for  the  Varley  loop  test. 

In  Fig.  156  the  faulty  wire  is  looped  with  a  good  conductor  at  the  distant 
station,  after  which  the  resistance  of  the  loop  thus  formed  is  measured  by 
the  regular  Wheatstone  bridge  method.  When  the  resistance  of  the  loop 
has  been  determined,  the  connections  for  the  Varley  test  are  made  as  shown 
in  Fig.  156. 


174  AMERICAN  TELEGRAPH  PRACTICE 

In  practice  the  best  results  are  obtained  when  the  arm  a  has  10  ohms 
resistance,  and  the  arm  b  100  ohms.  Obtain  a  balance  by  closing  both  keys 
repeatedly  while  the  resistance  of  the  rheostat  is  adjusted  until  the  galva- 
nometer needle  is  not  deflected.  The  resistance  to  the  fault  is  determined  by 
means  of  the  formula: 

(Ri+R)b 


Where  x  represents  resistance  to  fault. 
RI  represents  resistance  of  loop. 
R  represents  resistance  in  rheostat. 

a    represents  resistance  in  arm  a. 

b    represents  resistance  in  arm  b. 

To  illustrate:  If  the  loop  has  a  resistance  of  420  ohms  and  a  balance  is 
indicated  when  the  rheostat  has  a  resistance  of  2,560  ohms,  with  a  10  ohms, 
and  b  100  ohms,  then  the  resistance  to  the  fault  will  be: 

(420  4-  2560)  X  100  298000 

---  2,560=  -          -  —  2,560  =  2,700  —  2,560  =  149. 
10  +  100  no 

If  the  faulty  wire  is  a  No.  10  B.  &  S.,  gage  copper  conductor,  it  may  be 
ascertained  by  referring  to  the  table  of  wire  gages  (see  tables  in  appendix) 
that  its  resistance  is  5.28  ohms  per  mile  at  60°  F.,  which  for  all  practical 
purposes  is  sufficiently  accurate  at  all  ordinary  temperatures.  If  then  the 
resistance  to  the  fault  (149  ohms)  be  divided  by  the  resistance  per  mile, 
of  the  wire  (5.28  ohms),  the  quotient  28.2  miles  will  be  the  distance  to  the 
fault.  If  short  wires  are  used  between  the  bridge  and  the  conductors  tested, 
ascertain  the  resistance  of  the  short  wire  connected  to  the  faulty  wire  and 
deduct  its  resistance  from  the  total  resistance  to  the  fault. 

For  example:  had  connecting  wires  been  used  in  the  above  instance, 
and  that  connected  to  the  faulty  wire  found  to  measure  2  ohms  the  end  of 
the  formula  would  be  149  —  2  =  147  ohms  actual  resistance  to  the  fault. 

And     T^g  =  27.  8  miles  to  fault. 

Obviously,  any  measurement  made  in  the  above  described  manner,  may 
be  checked  for  accuracy  by  reversing  the  individual  "legs"  of  the  loop  in 
the  bridge,  and  computing  the  resistance  of,  or  the  distance  to  the  fault 
along  the  good  wire  and  back  along  the  faulty  wire. 

In  those  instances  where  there  are  indications  of  current  in  the  crossed 
wire  due  to  foreign  battery,  which  cannot  conveniently  be  eliminated, 
remove  the  regular  battery  from  the  testing  set  and  substitute  a  ground 
connection  in  its  place. 

In  making  Wheatstone  bridge  measurements,  the  battery  key  should 
be  closed  a  moment  or  so  in  advance  of  the  closing  of  the  galvanometer  key  ; 


RESISTANCE  MEASUREMENTS  175 

this  to  avoid  momentary  false  indications  of  the  needle.  Also,  care  should 
be  taken  to  have  current  in  the  bridge  coils  during  the  shortest  possible  time, 
in  order  to  avoid  charring  of  the  silk  insulation  of  the  wire. 

TO  MEASURE  THE  CONDUCTOR  RESISTANCE  OF  GROUND  RETURN  CIRCUITS 

Arrange  the  bridge  connections  as  shown  in  Fig.  148.  Adjust  the  bridge 
arms,  and  balance  as  previously  explained.  To  accurately  measure  the 
resistance  of  a  wire,  where  two  other  wires  between  the  same  points  are 
available,  proceed  as  follows: 

Suppose  it  is  desired  to  measure  the  resistance  of  the  wire  X,  Fig.  157. l 
Measure   separately  the   resistance  of  loops 
made  up  as  follows :  Y 

Wire  X  with  wire  F, 

Wire  X  with  wire  Z,  _ 

Wire  Y  with  wire  Z, 

If  the  first  loop  measures  90  ohms,  the  second  93  ohms,  and  the  third 
loop  99  ohms,  then  the  total  resistance  of  the  three  loops  is  282  ohms.  As 
each  of  the  wires  was  used  twice  in  making  up  the  loops  measured,  the  total 
resistance  of  the  three  wires  measured  once,  obviously  would  be  one-half 
of  282,  or  141  ohms;  and  as  the  resistance  of  the. loop  formed  of  the  two 
wires  Y  and  Z  is  known  to  be  99  ohms,  the  resistance  of  the  wire  X  is  obtained 
by  deducting  99  from  141,  leaving  42  ohms  as  the  resistance  of  X.  Once 
the  resistance  of  one  wire  is  known,  the  resistance  of  each  of  the  other  wires 
is  determined  by  looping  the  wire  of  known  resistance  with  the  wire  to  be 
measured  and  then  subtracting  the  resistance  of  the  first  wire  measured 
from  the  resistance  of  the  loop. 

METHOD  OF  LOCATING  "OPENS"  IN  CABLES 

An  excellent  test  in  cases  where  the  insulation  is  normal,  may  be  carried 
out  by  connecting  the  bridge  as  shown  in  Fig.  1 5  8 .  G  is  a  source  of  alternating 
current.  Where  current  from  an  alternating-current  dynamo  is  not  available, 
a  small  induction  coil  may  be  used  to  supply  the  desired  current.  Another 
convenient  method  of  providing  an  alternating-current  source,  is  to  connect 
two  double-contact  relays,  or  transmitters,  as  indicated  in  Fig.  159,  where  a 
source  of  direct  current  is  shown  connected  in  series  with  a  vibrating  bell  and 
the  windings  of  two  transmitters.  A  second  source  of  direct  current  is  con- 
nected with  the  local  contact  points  of  the  transmitters  in  the  manner  illus- 
trated. As  the  circuit  through  the  coils  of  the  transmitters  is  continuously 
opened  and  closed,  due  to  the  operation  of  the  vibrating  bell,  it  is  evident  that 
the  current  sent  out  on  the  lines  connected  to  the  respective  armatures  of  the 
transmitters,  will  be  alternating  in  character. 

1  "Examples  from  Postal  Telegraph- Cable  Co.'s  book  of  instructions." 


176 


AMERICAN  TELEGRAPH  PRACTICE 


For  cables  approximately  1,000  feet  in  length,  the  alternating-current 
generator  should  have  an  e.m.f.  of  from  40  to  130  volts,  and  the  arm  a  of  the 
bridge  may  have  a  resistance  of  100,  or  1,000  ohms.  The  capacity  of  a  con- 
ductor increases  as  its  length  is  increased:  the  greater  the  capacity  of  the 
conductor  under  test,  the  lower  should  be  the  voltage  of  the  testing  battery, 
and  the  lower  should  be  the  resistance  of  arm  a  of  the  bridge. 

M 

Good  Conductors  M 


Broken  or  Open  Conductor    K 

(rood  Conductor  adjacent  to  Broken     L 
Conductor. 


FIG.  158. — Method  of  locating  "opens"  in  cabled  conductors. 

To  locate  a  break  in  a  cable  conductor,  pick  out  three  good  conductors 
having  the  same  gage  as  the  open  wire  and  connect  them  as  shown  in  Fig. 
158.  The  conductors  selected  should  have  relations  as  shown  in  Fig.  158, 
that  is,  L  must  be  adjacent  to  K,  and  N  adjacent  to  M.  To  obtain  a  balance, 
open  the  four  wires  under  test  at  the  distant  end,  close  keys  GK  and  BK  and 
adjust  the  resistance  in  the  R  arm  of  the  bridge  until  no  sound,  or  at  least 
until  minimum  sound  is  heard  in  the  telephone  receiver  when  placed  to  the 
ear. 


D.C. 


FIG.  159. — Convenient  arrangement  for  supplying  an  alternating  current  for  testing 
purposes  where  an  alternating  current  dynamo  is  not  available. 


Then  the  distance  to  the  fault 


LXa 
R 


Where  X  represents  the  distance  in  feet,  to  fault, 

L  represents  the  length  of  the  cable  in  feet, 

a  represents  resistance  in  arm  a, 

R  represents  resistance  in  arm  R. 


THE  BLAVIER  TEST  177 

For  example:  Suppose  we  have  a  cable  5,280  ft.  in  length,  and  that  a  balance 
of  the  bridge  is  obtained  when  the  unplugged  resistance  in  the  R  arm  is 
1,872  ohms,  while  a  has  a  resistance  of  100  ohms.  Then  the  distance  from 
the  testing  station  to  the  fault  is: 

100 
-  =  282  ft. 


1872 

THE  BLAVIER  TEST 

A  method  known  as  the  Blavier,  sometimes  used  for  locating  a  partial 
ground  or  an  escape,  where  there  is  no  good  wire  available  for  looping  pur- 
poses, may  be  carried  out  as  follows: 

Let  r2  represent  the  total  resistance  of  the  conductor  under  test  (this 
must  be  known  from  previous  measurement,  obtained  from  a  wire  table,  or 
calculated  from  the  length,  size  and  conductivity  of  the  wire).  Let  R  repre- 
sent the  resistance  of  the  wire  with  the  distant  end  open,  and  ^  the  resist- 
ance of  the  wire  with  distant  end  grounded.  Then,  the  resistance  from  the 
testing  point  to  the  fault 


x  =  ri- 

By  dividing  x  by  the  resistance  per  unit  length  of  the  conductor,  obtained 
as  above  suggested,  the  distance  to  the  fault  is  arrived  at.  If  L  represents 
the  length  of  the  conductor  in  feet,  and  r2  the  normal  resistance  of  the  faulty 
wire  to  the  distant  end  of  the  line,  the  distance  in  feet  to  the  fault 

_xL 

rz 

The  accuracy  of  measurements  made  by  this  method  depends  upon  the 
resistance  of  the  fault  remaining  constant  during  each  measurement. 

There  are  instances  where  the  resistance  of  the  fault  is  so  high  or  so 
variable  that  the  Blavier  method  is  not  reliable,  and  in  general  it  is  found 
that  the  Murray  arrangement  (Fig.  158)  is  more  satisfactory,  where 
additional  good  conductors  are  available  for  the  test. 

THE  FISHER  LOOP  TEST 

This  test  may  be  used  in  cases  where  there  are  two  good  conductors  avail- 
able which  terminate  at  the  same  point  as  the  faulty  wire.  It  is  not  necessary 
that  the  resistances  of  the  conductors  be  equal,  so  the  good  wires  used  for  the 
test  may  be  in  another  cable,  or  may  be  open  aerial  wires. 

In  Fig.  1590  the  faulty  wire  C  and  the  good  wires  D  and  E  are  shown  con- 
nected at  the  distant  station  Y.  It  is  then  necessary  to  make  two  separate 
tests.  First,  one  side  of  the  battery  is  connected  to  the  sheath  as  shown  at 
12 


178 


AMERICAN  TELEGRAPH  PRACTICE 


X.  The  resistance  6*  is  adjusted  until  the  galvanometer  needle  shows  no  de- 
flection. The  resistance  values  of  R  and  5  are  noted.  Then  as  in  159^  the 
battery  is  connected  to  the  good  conductor  E,  and  a  balance  taken,  the  re- 
sistance values  being  noted  as  RI  and  Si.  Then  if  L  equals  the  length  of  the 
faulty  wire,  the  distance  to  the  fault  is  determined  by  the  formula 


In  cases  where  connecting  wires  are  used  between  the  testing  set  and  the 
actual  conductor  connections,  the  connecting  wire  entering  into  the  measure- 


c       * 


V' 

f£ 


FIG.  159. — Fisher  loop  test. 

ment  is  the  one  extending  from  the  bridge  to  the  faulty  wire.     In  the  Fisher 
tests,  the  same  rules  apply  in  locating  crosses  and  shorts  as  in  the  Murray  tests. 


ROUGH  TESTS 

When  a  wire  chief  has  become  thoroughly  familiar  with  the  electrical 
and  physical  characteristics  of  the  various  line  conductors  in  his  division  he 
is  in  a  position  to  apply  certain  rough  tests,  which  although  they  do  not 
produce  accurate  figures,  often  serve  to  restore  circuits  quickly,  especially 
where  trunk-line  facilities  are  limited. 

In  switch-board  parlance,  each  main-line  circuit  has  its  "feel,"  and 
a  wire  chief  familiar  with  the  peculiarities  of  a  particular  circuit,  can 


ROUGH  TESTS  179 

tell  by  "feeling"  it  whether  conditions  are  normal  or  abnormal.  Consider, 
for  instance,  a  line  wire  extending  between  two  terminal  stations  200 
miles  apart,  and  that  there  are  10  intermediate  offices  connected  into  the 
circuit,  each  intermediate  office  having  inserted  in  the  line  a  relay  of  150  ohms 
resistance.  If  the  circuit  is  opened  at  the  distant  terminal  (by  opening  the 
line  key  or  disconnecting  the  ground  wire)  then,  provided  battery  is  applied  to 
the  line  at  the  home  station,  when  the  home  key  is  closed  at  intervals,  as  in 
making  "dots"  slowly,  there  will  be  a  pronounced  "static"  kick  as  current 
momentarily  traverses  the  coils  of  the  home  relay,  causing  the  relay  armature 
to  be  attracted  to  an  extent  directly  dependent  upon  the  capacity  of  the  line 
wire,  and  upon  the  number  of  relays  included  in  the  circuit.  As  the  circuit  is 
open  it  is  evident  that  the  effect  on  the  home  relay  is  due  to  the  capacity  of  the 
line  wire,  which  means  that  the  longer  the  line  and  the  greater  the  number  of 
relays  in  circuit,  the  greater  will  be  the  force  producing  the  kick  of  the  home 
relay  armature.  Therefore  when  a  ground  return  circuit  opens  at  an  un- 
known point,  if  the  "kick"  of  the  relay  armature  has  about  the  same  strength, 
or  "feel"  as  when  the  line  key  at  the  distant  terminal  is  opened,  it  is  likely 
that  the  line  is  open  at  a  point  near  the  distant  terminal.  If,  however,  the 
kick  is  feeble,  the  line  is  open  near  the  home  station.  And  generally  the 
strength  of  kick  indicates  to  the  tester  the  approximate  distance  to  the  fault, 
enabling  him  to  call  in  an  intermediate  office  near  the  fault  on  another  wire. 
Thus,  time  is  saved  which  otherwise  would  be  consumed  in  tracing  the 
fault  from  station  to  station  along  the  line  from  the  terminal  office. 

Had  the  trouble  which  developed  on  the  line  been  the  result  of  an  acci- 
dental ground  contact  instead  of  an  "open,"  the  wire  chief's  knowledge  of  the 
normal  operating  characteristics  of  the  circuit  enables  him  to  apply  a 
rough  test  to  determine  the  approximate  location  of  the  ground.  Under 
normal  conditions  a  circuit  has  a  regular  e.m.f.  applied  to  it.  This,  with  the 
regular  resistance  of  line  plus  relay  resistance,  permits  of  a  definite  current 
value  in  the  circuit.  Normal  operating  current  produces  what  might  be 
called  "normal  pull"  on  the  armature  of  the  relay.  In  the  case  under  con- 
sideration, where  the  line  wire  is  supposed  to  be  "grounded"  at  an  unknown 
point  between  the  two  terminals  of  the  line,  if  it  is  found  that  the  magnetic 
"pull"  of  the  testing  relay  is  abnormally  strong,  it  is  evident  that  the  wire 
is  grounded  at  a  point  not  far  distant  from  the  home  station.  If  on  the 
other  hand  the  pull  is  about  normal,  the  ground  in  all  probability  will  be  found 
not  far  from  the  distant  terminal  of  the  line.  And,  in  general,  the  strength 
of  the  current  flowing  through  the  home  relay  indicates  to  the  tester  approx- 
imately the  distance  to  the  accidental  ground  contact. 

When  two  wires  entering  the  same  switchboard  become  "crossed"  some- 
where out  on  the  line,  it  is  not  always  immediately  apparent  which  two  are  in 
contact.  When  a  wire  shows  a  cross  with  another  circuit  carrying  current, 
the  identity  of  the  latter  may  be  ascertained  by  removing  the  regular  battery 


180  AMERICAN  TELEGRAPH  PRACTICE 

from  the  first  wire,  and  grounding  that  circuit  at  the  home  station  through 
a  test  relay  at  the  switchboard.  The  relay  thus  inserted  in  the  line  has  its 
winding  energized  by  a  current  which  enters  the  wire  at  the  " cross,"  and  the 
procedure  of  the  rough  test  is  to  open  consecutively  each  wire  which  follows 
the  same  pole  route,  until  one  is  found  which  when  opened  (thus  removing 
its  battery)  opens  also  the  wire  in  which  the  test  relay  is  inserted.  The  point 
at  which  the  cross  exists  may  be  located  by  having  intermediate  stations 
with  this  wire  cut  into  their  switchboards,  open  the  circuit  for  a  few  seconds. 
If  the  test  progresses  from  station  to  station  away  from  the  home  station,  the 
first  station  called  in,  whose  open  key  fails  to  open  the  test  relay,  is,  in  fact, 
the  first  station  beyond  the  cross,  and  the  point  at  which  the  fault  exists  has 
been  located  between  two  certain  stations. 

The  above  method  of  identifying  crossed  wires  is  applicable  only  where  the 
wires  involved  take  main  battery  at  the  testing  station  only,  or  in  cases  where 

main   battery  supplied  at  the- 
^  "\^  distant  terminal  is  temporarily 

removed  from  the  wires  affected. 
FIG.  160.  When  two  wires   are  crossed, 

and  until  the  cross  is   cleared 

by  a  lineman  detailed  for  that  purpose,  one  good  circuit  may  be  made  up  by 
having  a  station  on  each  side  of  the  cross  (in  each  case  as  close  to  the  cross  as 
possible)  open  the  least  important  circuit.  This  creates  a  condition  such  as 
that  shown  in  Fig.  160,  permitting  one  good  circuit  to  be  restored  to  service 
between  the  terminals  of  the  line. 


ALL  CIRCUITS  INTERRUPTED 

It  occasionally  happens,  due  to  storms,  sleet,  fire  or  other  cause,  that  all 
wires  on  a  route  are  at  a  certain  point  grounded,  crossed,  or  open.  Such  a 
condition  is  usually  referred  to  as  a  wreck.  When  this  happens,  the  wire 
chief  having  jurisdiction  over  this  particular  section,  is  called  upon  to  make 
good  as  many  circuits  as  possible  and  as  quickly  as  he  can.  In  the  language 
of  the  "board"  he  is  required  to  "dig  a  hole  through." 

The  arrangement  shown  in  Fig.  161  furnishes  a  means  for  obtaining 
quick  results  in  case  of  a  general  wreck  of  wires. 

It  may  be  seen  that  one  side  of  the  testing  relay  is  grounded.  The  test 
requires  that  the  other  side  of  the  relay  circuit  be  connected  in  turn  with  each 
of  the  line  conductors  involved.  While  the  relay  is  connected  in  series  with  a 
particular  wire,  all  other  wires  are  opened  at  the  home  switchboard,  and  bat- 
tery applied  to  the  wire  under  test.  The  closing  of  the  relay  armature  tongue 
indicates  a  cross  between  the  wire  connected  through  the  relay  and  the  wire 
to  which  the  battery  is  applied.  With  this  arrangement  it  is  possible  quickly 
to  ascertain  which  wires  are  crossed,  which  open,  which  grounded,  etc. 


ROUGH  TESTS 


181 


After  repairmen  arrive  at  the  wreck,  and  the  restoration  of  circuits  begins, 
it  is  of  considerable  advantage  to  employ  an  automatic  arrangement  at  the 
testing  office,  which  will  announce  to  the  wire  chief  when  a  fault  has  been 
cleared.  The  arrangement  illustrated  in  Fig.  162  is  extensively  employed 
for  this  purpose. 

Suppose,  for  instance,  that  the 
wire  shown  connected  to  the  relay 
through  the  main  switchboard  and 
spring-jack  is  grounded  through  a 
battery.  Switches  S  and  Si  are 
thrown  to  the  left,  thus  placing  the 
vibrating  bell  in  circuit  through  the 


Frc.  161. 


back  contacts  of  relay  R.  The  office 
first  beyond  G  (the  ground  contact) 
is  instructed  to  leave  the  grounded 
wire  open.  As  long  as  the  circuit  remains  grounded  at  the  point  G  the 
relay  R  is  energized  and  its  armature  remains  in  the  closed  position,  which 
leaves  the  bell  circuit  open.  As  soon,  however,  as  the  ground  at  G  is  lifted, 
relay  R  opens,  due  to  the  fact  that  the  circuit  is  open  at  the  station  first  beyond 
G,  and  immediately  the  signal  bell  announces  the  removal  of  the  ground  contact. 


T 


FIG.  162. — Wire  chief's  test  relay  and  signaling  bell  connected  to  announce  the  removal 
of  a  ground  contact  or  the  closing  of  a  break. 

Switches  5  and  S\  are  then  thrown  to  the  right,  which  places  the  regular  sounder 
in  circuit  in  place  of  the  signal  bell.  Had  the  wire  under  observation  been  open 
tinsead  of  grounded,  the  distant  terminal  station  would  have  been  instructed 
to  keep  his  end  of  the  wire  to  ground  until  advised  further,  and  the  switches 
at  the  home  station  would  have  been  disposed,  5  to  the  right,  and  S\  to  the 


182  AMERICAN  TELEGRAPH  PRACTICE 

left.  This  provides  that  when  the  repairman  closes  the  break,  relay  R  will 
be  energized  as  a  result  of  completion  of  the  circuit  from  the  home  battery 
to  the  ground  at  the  distant  terminal  of  the  wire.  In  this  case,  with  the 
switches  disposed  as  above  stated,  the  vibrating  bell  sounds  the  closing  of  the 
break. 

VOLTMETER  TESTS 

Voltmeters  haying  a  self-contained  series  resistance  of  about  2,000  ohms 
per  volt,  are  used  to  a  considerable  extent  for  line-testing  purposes.  The 
various  circuit  arrangements  employed  in  practice  are  shown  herewith. 

MEASURING  A  GROUND  CONTACT 

Connect  the  voltmeter  as  shown  in  Fig.  163,  with  one  side  of  the  testing 
battery  to  ground.  A  permanent  deflection  of  the  voltmeter  pointer  indicates 
a  "ground."  To  ascertain  the  value  of  the  resistance  to  ground,  note  the 


FIG.  163.  —  Voltmeter  method  of  measuring  a  ground  contact. 

reading  in  volts  with  key  K  open.  Call  this  figure  V.  Close  key  K,  note  the 
altered  reading  in  volts,  and  call  it  Vi.  Then,  where  R  is  the  resistance  of 
the  voltmeter,  the  resistance  to  the  ground  contact  on  the  line 


MEASUREMENT  OF  HIGH  RESISTANCE 

As  in  Fig.  164,  connect  the  resistance  to  be  measured  at  X  and  close  the 
switch  K  (thus  short  circuiting  X)  and  note  the  deflection  of  the  voltmeter 


I 1 1 iwwv- 

l~          X 


FIG.  164. — Voltmeter  method  of  measuring  high  resistances. 

pointer.     Call  this  Vi.     Open  the  switch  K  and  note  the  altered  deflection. 
Call  it  F2.     Then  the  resistance  value  desired 

•\/"  *  ~D 

A  = f^ «- 


R  representing  the  resistance  of  the  voltmeter. 


TESTING  WITH  VOLTMETER  183 

CAPACITY  TEST 

Connect  the  voltmeter  with  a  standard  condenser  C  as  shown  in  Fig.  165. 
First,  move  the  switch  to  position  i,  and  note  the  throw  in  degrees  of  the 
instrument  pointer.  Call  this  figure  Fi.  Then  place  the  switch  lever  on  2 


FIG.  165. — Voltmeter  method  of  measuring  the  capacity  of  a  conductor. 

and  again  note  the  deflection  of  the  pointer.  Call  this  figure  F2.  Then, 
the  capacity  of  the  line  =C  ~>  where  C  is  the  capacity  of  the  standard 
condenser  in  microfarads. 


MEASURING  ORDINARY  RESISTANCES 

For  the  purpose  of  measuring  ordinary  resistance  values,  such  as  instru- 
ment windings,  lines,  etc.,  connect  the  unknown  resistance  at  X  as  shown  in 
Fig.  1 66.  Shunt  the  voltmeter  with  a  resistance  S  having  a  value  such  that 


-/vwwv 


FIG.  1 66. — Voltmeter  method  of  measuring  ordinary  resistances. 

the  combined  resistance  of  the  voltmeter  and  the  shunt  will  have  some  con- 
venient value,  say  200  ohms.  (See  page  86  for  calculating  shunt  values.) 
The  measurement  is  then  made  in  the  same  way  as  in  the  case  of  a  high  resist- 
ance, and  the  value  is 

Fi-F2 

X=  ^ 200. 


ROUGH   VOLTMETER   METHOD    OF  LOCATING  A   CROSS 

Several  ingenius  arrangements  have  been  suggested  from  time  to  time, 
with  the  object  of  developing  a  satisfactory  voltmeter  loop  test.  It  is  found 
in  practice,  however,  that  the  voltmeter  is  not  as  adaptable  for  making 
accurate  measurements  with  looped  conductors  as  is  the  bridge  method 
previously  described. 

Referring  to  Fig.  167.     If  the  potential  at  the  point  L  where  the  line  con- 


184  AMERICAN  TELEGRAPH  PRACTICE 

ductor  enters  the  switchboard  is  150  volts,  obviously  there  is  a  gradual  drop 
of  potential  along  wire  A  until  the  point  G\  is  reached  where  the  potential  has 
fallen  to  zero.  If  a  cross  between  wires  A  and  B  exists  at  the  point  F  the 
drop  of  potential  at  that  point  may  be  ascertained  by  connecting  the  volt- 
meter in  series  with  the  home  end  of  the  wire  B  and  ground. 
Then  the  distance  from  the  testing  station  to  the  fault: 

Y_C-DE 
C 

Where  C  represents  the  voltage  at  L 
D  the  voltage  at  F  (or  P) 
E  the  distance  from  L  to  G. 

The  wire  B  must  be  left  open  at  the  distant  terminal  station,  or  at  an  office 
beyond  the  cross.     It  is  evident  that  errors  will  be  introduced,  due  to  any 


FIG.  167. — Voltmeter  loop  test. 

difference  of  potential  from  earth  currents  between  the  ground  connections 
G  and  Gi,  to  possible  high  resistance  at  the  fault  F,  to  the  resistance  of  the  wire 
B,  and  to  leakage.  The  extent  to  which  these  factors  introduce  error  is 
dependent  upon  the  resistance  of  the  voltmeter.  If  a  meter  having  a  re- 
sistance of  2,500  ohms  per  volt  is  used  for  the  test,  results  are  fairly 
accurate. 

INSULATION  RESISTANCE  OF  LINES 

With  any  form  of  construction  commercially  practicable,  perfect  insula- 
tion is  not  possible.  On  open  aerial  lines  although  electrostatic  and  electro- 
magnetic induction  takes  place,  there  is  no  current  leakage  from  wire  to 
wire  through  the  air,  but  at  every  point  at  which  wires  are  supported,  even 
with  the  best  construction  there  will  be  some  leakage  from  wire  to  wire  and 
from  wire  to  ground.  At  every  pole  there  exists  a  leak  to  earth.  The 
electrical  resistance  of  this  leak  is  high  if  the  wire  is  well  insulated,  and  low 
if  the  insulation  is  poor. 

At  the  point  of  support  the  wire  is  separated  from  the  cross-arm  or  pole 
by  an  insulator,  and  the  effective  insulation  of  the  line  is  dependent  upon  the 
construction,  shape,  material  and  condition  of  these  insulators;  also  upon  the 


INSULATION  RESISTANCE  OF  LINES  185 

space  along  the  cross-arm  separating  the  insulator  from  the  pole.  Glass  of 
certain  grades  offers  the  highest  insulation  to  electrical  conduction  through 
its  mass  of  any  commercially  available  material.  For  the  purposes  of 
telegraph  insulation,  glass  does  not  ideally  meet  the  rquirements,  due  to  the 
fact  that  surface  conduction  plays  an  important  part  in  leakage  from  line 
to  wooden  support.  Glass  is  highly  hygroscopic,  and  in  almost  every  state 
of  the  weather  and  of  the  atmosphere  it  becomes  coated  with  a  film  of 
moisture1  or  of  gross  matter.  Certain  grades  of  porcelain,  in  this  regard, 
meet  the  requirements  more  satisfactorily,  as  porcelain  is  not  as  hygroscopic 
as  glass,  and  rain  runs  readily  from  its  highly  glazed  surface. 

Many  attempts  have  been  made  to  explain  the  peculiar  behavior  of  leak- 
age of  electric  currents  over  the  surface  of  insulators  on  which  moisture  has 
condensed  due  to  exposure  to  ordinary  atmospheric  conditions.  Whether 
the  potential  applied  to  the  conductor  is  of  one  polarity,  or  is  alternating 
from  positive  to  negative  continuously  or  occasionally,  seems  to  play  an 
important  part  in  varying  the  electrical  resistance  of  the  film* of  moisture 
deposited.  In  some  cases  it  is  found  that  the  resistance  is  enormously 
greater  when  the  current  passes  in  one  direction  than  when  it  passes  in  the 
opposite  direction.  Apparently  the  nature  of  the  oxide  formed  on  the  con- 
ductor as  a  result  of  electrochemical  action  between  the  metal  of  the  con- 
ductor and  the  moisture  film,  undergoes  a  change  as  the  current  in  the 
conductor  is  reversed.  Duration  of  contact  of  either  polarity,  as  well  as 
rapidity  of  reversal,  probably  are  the  factors  which  determine  the  resistance 
between  the  wire  and  its  support,  across  the  surface  of  the  insulator,  assum- 
ing, of  course,  that  a  film  of  moisture  is  present.  The  hygrometric  state  of 
the  surrounding  atmosphere,  varying,  as  it  does,  naturally  accounts  for 
the  variations  in  the  thickness  of  the  film  of  moisture,  and  this  in  turn  has  a 
direct  bearing  upon  the  initial  resistance  when  battery  is  applied  to  the  line, 
irrespective  of  polarity. 

The  American  Telegraph  and  Telephone  Company  has  considered  a 
clear  weather  insulation  of  10  megohms  per  mile  as  satisfactory.  The 
Western  Union  Telegraph  Company  has  a  standard  of  50  megohms  per  mile, 
while  the  Postal  Telegraph- Cable  Company  aims  to  maintain  an  insulation  of 
100  megohms  per  mile  in  clear  weather.  Wet  weather  conditions,  however, 
greatly  reduce  these  figures,  and  when  a  drizzly  rain  and  fog  prevails  for 
any  considerable  length  of  time,  it  is  found  that  the  insulation  resistance  of 
lines  may  drop  lower  then  one  megohm  per  mile.  A  low-lying  dense  fog  has 
a  most  pronounced  effect  in  reducing  the  insulation  resistance  of  a  line,  and 
the  hygroscopic  characteristics  of  glass  insulators  are  clearly  evidenced  when 

1  The  large  amount  of  common  salt  (chloride  of  sodium)  floating  about  in  the  form  of 
fine  particles  in  the  air  results  in  condensation  upon  the  surface  of  all  exposed  bodies. 
Where  these  deposits  are  made  upon  the  surface  of  insulators,  the  saline  film  thus  formed 
is  a  much  better  conductor  of  electricity  than  is  the  insulator. 


186 


AMERICAN  TELEGRAPH  PRACTICE 


wires  are  thus  weather-bound,  by  the  fact  that  during  a  dense  fog,  should 
there  be  a  fairly  heavy  rain-fall  lasting  a  few  minutes,  the  insulation  resistance 
of  the  line  rapidly  increases.  So  much  so,  that  while  the  rain  continues  the 
insulation  has  been  known  to  closely  approach  clear  weather  values.  It  is 
hardly  likely  that  the  dripping  of  the  rain  from  the  surface  of  the  insulator 
produces  a  hydro-kinetic  effect  which  clears  the  moisture  condensed  on  the 
inner  surface  of  the  petticoat  insulator,  so  that,  so  far  as  investigation 
accounts  for  the  phenomena  observed,  nothing  is  explained  except  that  the 
exterior  surface  of  the  insulator  has  been  washed  clean. 

In  addition  to  insulator  leakage,  other  causes  bring  about  a  lowering  of 
insulation  resistance,  such  as  contact  between  wires  and  limbs  of  trees,  kite 
strings  (the  latter  when  wet  sometimes  causing  leakage  from  wire  to  wire), 
broken  insulators,  permitting  direct  contact  between  wire  and  cross-arm, 
surface  leakage  along  the  surface  of  bridle  wires  resting  against  cross-arms, 
etc.  All  of  these  avenues  of  escape  are  more  effective  as  leaks  during  wet 
weather. 

The  foregoing  has  been  introduced  at  this  time  so  that  an  understanding 
of  the  various  causes  which  permit  leakage  of  current  may  be  gathered. 


Mil-AM-Meter 
B  C 


FIG.  168. 


The  insulation  resistance  of  a  line  wire  may  be  measured  by  ascertaining 
the  resistance  at  the  terminal  A  while  the  distant  end  X  is  open,  or  insulated, 
as  in  Fig.  168. 

Under  such  conditions,  the  insulation  resistance  observed  does  not  equal 
the  sum  of  the  several  insulation  resistances  from  B  to  G\,  C  to  Gz,  D  to  6*3, 
E  to  £4,  and  F  to  G5.  Correctly  considered  the  insulation  resistance  ob- 
served is  that  of  the  circuits  ABGi,  BCG2,  CDG3,  DEC*,  and  EFG5,  and  at 
once  it  is  apparent  that  as  each  pole  or  support  unavoidably  constitutes  a 
leak  to  earth,  the  total  insulation  resistance  of  the  line  has  the  same  relation 
to  the  joint-conductivity  of  the  various  leak  paths  to  ground,  as  obtain  in 
all  other  problems  concerning  joint-conductivity,  and  which  have  been 
considered  in  an  earlier  chapter. 


ME  A  S  URING  INS  ULA  TION  RESIST  A  NCE  1 87 

MEASUREMENT  OF  INSULATION  RESISTANCE 

The  voltmeter  is  used  quite  extensively  in  making  insulation  measure- 
ments, but  it  should  be  remembered  that,  inasmuch  as  the  resistance  to  ground 

Vr-V* 

X=  —y — R}  as  explained  in  connection  with  Fig.  164,  the  resistance  per 

volt  of  the  meter  is  of  the  first  importance. 

A  voltmeter  having  a  range  of  100  volts,  and  a  resistance  of  100  ohms  per 
volt,  could  not  be  used  satisfactorily  in  measuring  resistances  as  high  as  one 
megohm.  The  highest  resistance  that  can  be  measured  with  such  a  meter  is 

TOO- i 
-  •  i  x  =  ~~    —10,000  =  990,000  ohms. 

It  follows  that  with  a  loo-volt  meter  having  a  resistance  of  206  ohms  per  volt, 
the  highest  resistance  which  can  be  measured  is  1,980,000  ohms. 

INSULATION  RESISTANCE  MEASUREMENTS  WITH  MILAMMETER 

One  method  of  measuring  the  insulation  resistance  of  lines,  which  has  been 
used  with  success,  makes  use  of  a  milammeter  in  connection  with  the  quad- 
ruplex  "long-end"  potential  of  375  volts  negative,  as  shown  in  Fig.  169. 

M.  A.  Meter 
375-T      H?°r  rl  Line 


FIG.  169. — Measuring  the  insulation  resistance  of  a  line.     Milammeter  method. 

To  measure  insulation  resistance,  the  lower  scale  of  a  standard  milammeter 
(five  divisions  equal  to  one  milampere)  is  used.  The  meter  is  inserted  in 
series  with  a  25,ooo-ohm  resistance  unit  and  connected  directly  to  the  line 
to  be  measured,  as  shown. 

The  25,ooo-ohm  coil  serves  to  protect  the  meter  from  damage  in  case  the 
line  under  test  is  grounded  close  by.  Its  presence  also  minimizes  the  effects 
of  induced  currents,  and  this  results  in  steadier  action  of  the  indicating  needle. 
With  a  potential  of  375  volts  and  a  resistance  of  25,000  ohms  the  milammeter 
needle  travels  exactly  the  full  length  of  the  scale,  in  accordance  with  Ohm's 
law.  The  insertion  of  any  additional  resistance,  such  as  that  of  a  line,  reduces 
the  amount  of  deflection. 

To  minimize  the  work  in  computing  the  insulation  resistance  in  ohms',  the 
reference  table  given  herewith,  is  used.  The  column  of  figures  at  the  extreme 
left,  reading  from  30  to  500,  refers  to  length  of  line  in  miles,  while  the  row  of 
figures  at  the  top,  reading  from  i  to  75,  refers  to  divisions  deflection  on  the 


188 


AMERICAN  TELEGRAPH  PRACTICE 


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sajiui  ui  9ifM  jo  ipSuarj 

MEASURING  INSULATION  RESISTANCE  189 

lower  scale  of  the  milammeter.  The  figures  in  the  body  of  the  table  represent 
approximately  the  insulation  resistance  in  megohms  per  mile.  The  procedure 
is  as  follows :  select  the  figure  in  the  left-hand  vertical  column  nearest  to  the 
length  of  the  line  under  test,  and  the  figure  in  the  top  row  nearest  to  the 
observed  deflection  in  divisions  of  the  milammeter  scale,  then  the  figure 
found  in  the  body  of  the  table  at  the  intersection  of  these  two  columns  will 
be  the  approximate  insulation  resistance  in  megohms  per  mile  of  the  wire 
measured. 

For  example:  with  a  line  wire  290  miles  long,  take  the  nearest  mileage 
shown  in  the  table,  viz.,  300.  With  10  divisions  deflection  the  resistance  is, 
according  to  the  table,  49  megohms  per  mile.  It  is  possible,  of  course,  to  ob- 
tain practically  the  same  results  by  employing  much  lower  potentials,  say  no 
or  130  volts.  In  this  case  the  25,ooo-ohm  series  resistance  may  be  omitted. 
One  degree  deflection  on  the  upper  scale  of  the  milammeter  represents  five 
milliamperes  current.  Five  milliamperes  with  130  volts  indicates  a  resist- 
ance of  26,000  ohms 

for  R  =  —r  =  —^ —  =  26,000. 

/     0.005 

And  if  the  line  is  100  miles  in  length,  the  insulation  resistance  per  mile 
=  26,000X100  =  2.6  megohms. 

During  wet  weather  the  wire  under  test  may  have  a  low-voltage  e.m.f.  im- 
pressed on  it  due  to  conduction  leakage  from  neighboring  wires  which  are 
carrying  current.  This  leakage  might  be  through  water-soaked  kite  strings, 
along  the  water-soaked  wooden  supports,  or  through  limbs  or  leaves  of  trees 
upon  which  both  wires  may  rest.  The  presence  of  foreign  current  in  the  con- 
ductor, obviously  alters  the  value  of  the  potential  applied  to  it  at  the  testing 
station:  increasing  or  decreasing  the  true  deflection  as  the  applied  and 
foreign  e.m.fs.  are  of  the  same  or  of  opposite  signs.  If  this  is  found  to  be  the 
case  it  is  well  to  place  to  line  the  polarity  which  gives  the  greater  deflection. 

The  case  above  cited,  where  the  insulation  resistance  per  mile  of  a  100- 
mile  line  was  shown  to  be  2.6  megohms,  should  not  be  taken  to  mean  that 
the  various  leak  paths  from  line  to  earth  are  evenly  distributed,  but  should 
be  regarded  as  the  average  for  the  entire  line.  In  Fig.  168  the  resistance  of 
the  paths  B,  C,  D,  E  and  F  to  ground  in  each  instance  may  have  equal 
resistances,  in  which  case  the  leakage  will  be  uniformly  distributed  along 
the  length  of  the  line.  In  practice,  however,  it  is  more  generally  experienced 
that  when  a  low  insulation  resistance  is  presented  between  line  and  ground, 
the  leak  will  be  found  to  be  unevenly  distributed.  That  is,  the  leak  paths 
to  ground  are  found  to  vary  greatly  in  their  individual  resistance.  In  most 
cases  where  an  abnormally  low  average  value  obtains,  the  larger  part  of  the 
leak  will  be  found  to  exist  at  a  particular  point. 


190  AMERICAN  TELEGRAPH  PRACTICE 

Referring  again  to  Fig.  168.  Suppose  that  when  the  line  is  opened  at  the 
distant  terminal  X,  the  milammeter  reading  indicates  an  excessive  leak  of 
current  to  ground.  By  having  the  different  offices  with  this  wire  in  their 
switchboards,  in  turn  open  the  wire  (progressing  from  office  to  office  in  a 
direction  away  from  X),  it  may  easily  be  ascertained  between  which  two 
offices  the  heavy  leak  exists.  For  instance,  should  the  milammeter  needle 
show  a  deflection  of  10  divisions  when  the  wire  is  open  at  X  only,  and  change 
very  little  as  keys  are  opened  at  offices  between  X  and  F,  and  F  and  E,  it  is 
evident  that  the  fault  exists  somewhere  between  F  and  A .  Should  an  open 
key  at  the  office  between  E  and  D  result  in  a  pronounced  reduction  in  the 
deflection  of  the  needle,  the  bulk  of  the  escape  will  be  found  at  a  point  some- 
where between  that  office  and  the  office  next  toward  X. 

INSULATION  RESISTANCE  OF  DISTANT  SECTIONS 

There  are  instances  where  it  is  necessary  for  a  wire  chief  to  measure  the 
insulation  resistance  of  remote  sections  of  a  line,  as  from  Y  to  Z,  Fig.  170. 
Two  separate  insulation  measurements  are  made  by  either  of  the  methods 
previously  described.  The  first  with  the  line  opened  at  Y,  and  the  second 
measurement  with  the  line  extending  through  to  Z  and  opened  at  that  end. 


X  Y  Z 

o  -  o  -  o 


FIG.  170. 
Then  the  insulation  resistance  of  the  section  Y-Z 


where  RI  represents  the  insulation  resistance  of  the  section  X-Y,  and  R% 
the  insulation  resistance  of  the  entire  line  X-Y-Z.  The  insulation  resistance 
of  the  section  Y-Z  in  megohms  per  mile, 

x=  RXD 

I  000000 

where  D  represents  the  length  in  miles  of  the  section  Y-Z. 

CONDUCTIVITY  MEASUREMENTS 

The  Wheatstone  bridge  method  of  measuring  the  conductivity  of  a  line 
was  explained  in  connection  with  Fig.  157,  and  that  method  should  be  used 
where  accurate  measurements  are  desired. 

Voltmeter-ammeter  Method.  —  Approximate  figures  may  be  obtained 


CONDUCTIVITY  MEASUREMENTS 


191 


more  quickly  by  means  of  the  voltmeter-ammeter  method  as  follows:  the 
wire  to  be  measured  is  grounded  at  the  distant  station  and  an  e.m.f. 
of  about  125  volts  applied  to  it  at  the  testing  station.  Through  the 
medium  of  the  spring-jack  at  the  switchboard  there  is  included  directly  in 
the  circuit  a  milammeter  as  shown  in  Fig.  171.  After  the  value  of  the  cur- 
rent flowing  has  been  noted,  the  milammeter  is  disconnected  from  the 
circuit  and  a  voltmeter  with  one  terminal  grounded,  is  connected  with  the 
line  contact  of  the  spring-jack.  The  reading  in  volts  is  noted.  Thus, 


VM 


FIG.  171. — Measuring  the  conductivity  of  a  line  by  the  voltmeter-ammeter  method. 

having  the  current  and  voltage  values  obtaining  in  the  circuit,  the  resistance 
may  be  calculated  by  Ohm's  law,  or  the  conductivity  of  the  line,  in  ohms 


r' 

/  (in  milhamperes) 

The  two  readings  of  voltage  and  current  should  be  taken,  one  immedi- 
ately after  the  other,  in  order  to  minimize  the  probability  of  error. 


MISCELLANEOUS  TESTS 
LOCATING  ALTERNATING   CURRENT  CROSSES 

A  method  of  locating  alternating  current  crosses  on  telegraph  lines,  sug- 
gested by  A.  J.  Eaves,  is  illustrated  in  the  schematic  diagram,  Fig.  172. 

Disconnect  the  battery  wires  of  a  Wheatstone  bridge  set  at  c  and  d,  and 
ground  the  point  c  through  a  resistance  AR  sufficient  to  reduce  the  incoming 
alternating  current  below  the  danger  point,  and  then  substitute  for  the  gal- 
vanometer of  the  set  an  alternating  current  milammeter,  shunted  with  about 
10  ohms  resistance,  S,  as  a  protection  to  the  instrument.  Balance  the  bridge 
by  inserting  resistance  in  the  rheostat  portion  of  the  bridge  until  the  needle 
points  to  zero,  on  the  lower  scale  of  the  milammeter.  This  indicates  that  no 
current  flows  between  f  and  g.  Then  half  of  the  resistance  of  R  will  be  equal 
to  the  distance  in  ohms  from  the  point  where  the  crossed  wire  is  looped  with 
the  good  wire  to  the  alternating  current  cross,  where  the  two  wires  are  of 


192 


AMERICAN  TELEGRAPH  PRACTICE 


approximately  the  same  resistance.  To  determine  the  distance  in  miles 
from  the  test  station  to  the  cross,  make  a  loop  measurement  of  the  good  and 
crossed  wires  before  the  battery  wires  are  disconnected  from  the  bridge,  and 
use  the  Varley  formula: 

7     *'-*, 

z  =        — » 


FIG.  172. — Method  of  locating  a  cross  between  a  telegraph  line  and  an  alternating-current 

line. 

where  Z  =  resistance  from  testing  station  to  cross, 

D  =  length  of  the  loop  in  miles, 

Ri  =  resistance  of  loop  in  ohms, 

R  =  resistance  of  rheostat  when  bridge  is  balanced. 
Then  the  distance  in  miles  from  the  test  station  to  the  cross  is 

V_ZXD 

' —    P 

By  using  a  telephone  receiver  instead  of  an  alternating-current  milammeter, 
the  same  result  can  be  obtained  by  inserting  resistance  in  the  rheostat  R 
until  no  noise,  or  until  minimum  sound  is  heard  in  the  receiver. 

WESTERN  UNION  PROPORTIONAL  TEST  SET 

Within  recent  years  several  different  makes  of  testing  set  have  been  intro- 
duced, which  have  been  designed  with  the  object  of  reducing  to  a  minimum 
the  amount  of  calculation  necessary  to  locate  faults. 

A  set  of  this  kind,  which  has  been,  adopted  by  the  Western  Union  Tele- 
graph Company  for  the  use  of  linemen  and  cable  testers  has  its  circuits 
arranged  as  shown  in  Fig.  173.  This  set  consists  of  a  simplified  rheostat,  a 
galvanometer  and  a  battery  contained  in  a  box  7X9X5  in.  in  size.  The 
component  parts  of  the  apparatus,  with  their  connections,  are  shown  in  Fig. 
173,  where  GS  is  a  galvanometer  shunt,  R  a  rheostat  with  a  radial  contact 
arm,  BK  a  battery  key,  and  SK  a  shunt  key. 


W.  U.  PROPORTIONAL  TEST  SET 


193 


Locating  a  Cross  or  a  Ground. — Select  a  good  conductor  having  the 
same  gage  as  that  of  the  faulty  wire,  preferably  one  running  along  the  same 
route,  or  in  the  same  cable.  Connect  the  good  conductor  to  the  binding 


FIG.  173. — Circuits  of  the  Western  Union  proportional  test  set. 

post  G  of  the  set,  and  the  faulty  wire  to  the  binding  post  L.  Have  the 
distant  station  or  testing  point  connect  the  ends  of  the  two  wires  together 
as  in  looping.  If  the  trouble  is  a  cross,  connect  the  other  crossed  wire  to 
the  binding  post  GR.  If  a  ground,  connect  the  post  GR  to  the  home 


'000ft 


iHHHhf 


FIG.  174. — Locating  a  ground  contact  with  the  W.  U.  proportional  test  set. 

ground.  Move  the  radial  arm  over  the  contact  buttons  around  the  circle 
until  a  point  is  reached  where  closing  the  key  BK  does  not  result  in  a 
deflection  of  the  galvanometer  needle.  Now  close  both  battery  and  shunt 
keys,  and  if  the  needle  is  deflected,  move  the  arm  to  a  contact  where  the 

13 


194  AMERICAN  TELEGRAPH  PRACTICE 

needle  shows  the  least  movement.  As  the  contact  buttons  are  numbered 
from  i  to  50,  multiply  the  number  of  the  button  at  which  minimum  deflec- 
tion is  observed  by  the  total  length  in  feet  of  the  loop,  and  divide  by  100; 
this  will  give  the  distance  in  feet  from  the  testing  point  to  the  fault. 

Example :  in  locating  a  ground,  suppose  a  loop  is  made  up  having  a  total 
length  of  2,000  ft.,  Fig.  174,  and  a  balance  is  obtained  when  the  arm  rests  on 
contact  No.  38,  then  the  distance  to  the  fault  is 

38X2000 

—  =  760  ft. 
100          ' 


FIG.  175. — Locating  a  "cross"  with  the  W.  U.  proportional  test  set. 

If  in  locating  a  cross,  a  loop  is  made  up  having  a  total  length  of  1,600  ft., 
as  in  Fig.  175,  and  a  balance  is  obtained  when  the  arm  rests  on  contact  No. 
28,  then  the  distance  to  the  fault  is 

\/"\/"v 

=  4-4-8  ft. 


100 

INEQUALITIES  IN  LINE  RESISTANCE 

Fault  locating  by  loop  methods;  generally  is  based  on  the  assumption 
that  the  conductors  employed  are  of  uniform  resistance  per  unit  length.  In 
many  instances  this  is  not  true,  and  unless  the  wire  inequalities  balance  each 
other,  the  working  out  of  formulae  will  not  always  give  exact  locations.  For- 
tunately, in  most  cases  inequalities  are  distributed  so  that  one  compensates 
for  another,  thus  evening  up  the  resistance  to  a  value  approximately  that  of 
the  calculation.  Inequalities  may  consist  of  introduced  resistances,  such  as 
those  resulting  from  poorly  soldered  sleeves,  variations  in  gage  of  the  con- 
ductors used,  and  variations  in  temperature  of  different  portions  of  the  line. 

USING  CONDUCTORS  OF  MIXED  GAGES 

In  those  instances  where  it  is  necessary  to  use  cable  conductors  of  different 
gages  in  making  up  loops  for  measurement  purposes,  it  is  customary  to 


TELEPHONE  RECEIVER  TESTS  195 

compute  a  scale  of  coefficient  values,  such  for  instance  as  might  be  used  to 
change  a  conductor  of  a  certain  gage  into  resistance-feet-equivalents  of  the 
other  wire  available. 

Where  conductors  of  14  and  16  gage  are  concerned,  the  desired  ends  may 
be  attained  by  multiplying  the  given  number  of  feet  of  16  gage  by  the  coeffi- 
cient 1.59,  which  changes  it  into  the  number  of  feet  that  would  be  required 
to  make  up  the  same  resistance  in  cases  where  a  i4-gage  conductor  is  used. 
No.  14  gage  likewise  may  be  changed  to  16  gage,  for  the  purposes  of  measure- 
ment, by  employing  the  coefficient  0.625. 

TELEPHONE  RECEIVER  TESTS 

For  making  qualitative  tests,  the  telephone  receiver  has,  due  to  its  great 
sensibility  to  weak  currents,  come  into  quite  general  use  in  locating  faults  in 
cables. 

A  tester  who  has  had  experience  with  the  telephone  receiver  as  a  testing 
instrument  recognizes  several  different  tones  or  "  clicks"  when  the  receiver 
is  connected  directly  in  a  circuit  supplied  with  battery,  or  when  the  receiver 
is  connected  inductively  with  another  circuit. 

When  a  receiver  and  a  source  of  current  are  directly  connected  through  a 
low  resistance,  each  time  the  circuit  is  closed  and  opened,  the  diaphragm  of 
the  receiver  is  attracted  and  released,  respectively,  and  this  movement  of 
the  diaphragm  results  in  an  audible  click  varying  in  intensity  according 
to  the  amount  of  resistance  of  the  circuit.  The  click  in  this  case  is  quite 
sharp  and  pronounced  and  is  recognized  as  a  closed-circuit  or  "battery" 
click. 

In  cases  where  the  receiver  and  the  battery  are  connected  through  a  high 
resistance,  say,  in  the  neighborhood  of  a  megohm,  the  click  will  still  be  audi- 
ble, but  not  intense  or  sharp.  In  a  circuit  of  this  kind  the  sound  heard  is 
recognized  as  a  "leak"  click. 

If  a  receiver  is  connected  in  circuit  with  a  long  aerial  or  cabled  conductor, 
even  if  the  wire  is  open  at  some  distant  point,  a  sound  is  heard  in  the  receiver 
which  is  recognized  as  a  "capacity"  click.  It  is  caused  by  the  charging  or 
discharging  of  the  line  through  the  coils  of  the  receiver.  Still  another  char- 
acteristic click  heard  in  the  receiver  is  recognized  as  due  to  induction  from 
neighboring  parallel  circuits  which  are  carrying  interrupted  currents,  or 
currents  which  are  being  reversed  in  polarity  at  regular  or  irregular 
intervals. 

In  several  tests  heretofore  described,  where  a  telephone  receiver  was  sub- 
stituted for  the  galvanometer  in  "bridge"  measurements,  the  receiver  was 
availed  of  to  indicate  "no  current"  or  minimum  difference  of  potential.  In 
the  "tone"  tests  now  under  consideration  the  receiver  is  required  to  indicate 
the  conditions  obtaining  in  the  circuit  being  tested,  by  differences  in  the  vol- 
ume of  sound  produced,  or  by  characteristic  "tones"  regardless  of  volume. 


196  AMERICAN  TELEGRAPH  PRACTICE 

TESTING  FUSES  WITH  THE  RECEIVER 

If  the  receiver  is  equipped  with  a  double-conducting  cord  having  two  free 
terminals,  fuses  may  be  tested  without  removing  them  from  the  fuse  blocks, 
simply  by  touching  the  two  terminals  of  the  cord  to  the  fuse  terminals.  The 
" battery"  click  indicates  that  the  fuse  is  burned  out,  or  open. 

TESTING  LINE  CONDUCTORS 

In  testing  ground-return  circuits,  the  receiver  may  be  connected  in  series 
with  a  battery  which  has  one  terminal  grounded  as  in  Fig.  176.  If  the  bat- 
tery click  is  heard  in  the  receiver  when  the  other  terminal  of  the  receiver  is 
connected  to  the  line  wire,  the  indication  means  that  the  conductor  is  grounded . 
The  " capacity"  click  would  indicate  that  the  circuit  is  "open,"  while  the 

"leak"  click  would  indicate  that 
the  line  is  grounded  through  a 
high  resistance.  Obviously  the 

-=-  strength  of  the  "capacity"  click 

would   indicate   roughly  the  dis- 
i-  i     tance  to  the  point  at  which  the  line 

FIG.    i76.-Circuit  testing  with  telephone       is     °Pen'    and     the     strength    °f 
receiver.  the      leak"   click  would  indicate 

roughly    the    resistance  value  of 
the  leak  to  ground. 

In  cabled  conductors  crosses  may  occur  between  individual  circuits  due 
to  break-down  of  the  insulation  between  the  wires,  to  wearing  away  of  the 
insulation  due  to  vibration,  to  crystallization  of  the  lead  sheath  which  permits 
moisture  to  enter,  to  lightning  and  to  various  other  causes.  Grounding  of  a 
conductor  occurs  when  an  uninsulated  portion  of  the  wire  comes  into  contact 
with  the  lead  sheath. 

LOCATING  GROUNDS  AND  CROSSES  WITH  THE  RECEIVER 

The  testing  circuit  is  made  up  of  a  dry-cell  battery  and  a  telephone  re- 
ceiver in  series,  one  end  of  the  circuit  being  connected  with  the  sheath  of  the 
cable,  while  the  other  terminal  of  the  circuit  is  placed  in  contact  with  the  wire 
to  be  tested.  At  the  end  of  the  cable  from  which  the  test  is  being  conducted, 
all  other  wires  should  be  "bunched"  and  connected  with  the  sheath.  At  the 
distant  end  of  the  cable  all  wires  are  left  "open"  then,  touching  the  metal 
tip  of  the  receiver  cord  to  the  various  conductors  will  quickly  develop  whether 
any  of  them  are  crossed  or  grounded.  The  "click"  peculiar  to  each  kind  of 
fault  indicates  the  nature  of  the  interruption. 

CONTINUITY  TESTS  WITH  THE  RECEIVER 

Tests  for  continuity  require  that  all  wires  be  bunched  at  the  distant  end 
of  the  cable  and  there  connected  to  a  separate  wire  in  another  cable,  which 


FAULT-FINDERS  197 

extends  back  to  the  point  from  which  the  test  is  being  made.  The  spare  wire 
is  connected  to  one  terminal  of  the  testing  circuit  as  shown  in  Fig.  177. 
The  other  terminal  of  the  testing  circuit,  then  may  be  connected  successively 
to  the  ends  of  the  various  conductors  at  the  testing  station. 

If,  when  the  metal  tip  of  the  receiver  cord  is  repeatedly  touched  to  the  end 
of  a  wire,  the  clicks  continue  without  diminishing  in  intensity;  the  circuit  is 
continuous,  while  the  cessation  of 
the   clicks   after   a   few   contacts        f"\=| 
have  been  made,  indicates  that  the       © 
circuit  is  open.     The  two  or  three      -r- 

clicks  heard  in  this  case,  are  due  to 
,      ,  .     ,  .          .  FIG.  177. — Continuity  test  with  telephone 

the  battery  of  the  testing  circuit  receiver. 

charging  the  conductor  under  test. 

Continuity  tests  are  frequently  made  with  a  vibrating  bell  or  a  buzzer 
in  place  of  a  telephone  receiver,  and  although  more  battery  is  required  in 
making  the  test,  the  buzzer  gives  a  more  definite  signal,  and  is  not  likely  to 
record  static  impulses. 


FAULT-FINDERS 

There  are  several  telephone  "  fault-finder "  testing  sets  in  common  use 
which  are  based  on  the  principle  that  if  an  interrupted  current  is  continuously 
sent  out  over  cabled  conductors,  the  "tone"  peculiar  to  the  interrupted 
current  thus  impressed  on  the  conductors  may  be  detected  at  any  point 
along  the  cable  by  means  of  exploring  coils,  or  detector  coils  especially 
designed  for  the  purpose. 

Among  these  might  be  mentioned  the  Matthews'  "Telafault,"  and  the 
"  Wireless  Trouble  Finder." 


THE  MATTHEWS'  TELAFAULT 

The  Telafault  is  a  self-contained  cable  testing  set,  designed  for  locating 
trouble  in  telegraph  and  telephone  cables.  By  means  of  this  set,  low 
resistance  crosses,  grounds  and  shorts,  can  be  readily  located  by  the  cable 
tester  or  trouble-man,  and  where  the  test  is  properly  made,  the  fault  can  be 
located  closely. 

The  schematic  arrangement  of  the  circuits  of  this  test  set  is  shown  in 
Fig.  178.  Included  as  a  part  of  the  set,  there  is  an  " exploring"  coil,  the 
terminals  of  which  are  connected  with  a  telephone  receiver  fitted  with  a 
head-band.  Closing  the  battery  switch  S  starts  the  interrupter,  and  when 
two  cable  conductors  are  connected  with  the  binding-posts  A  and  B,  an 
interrupted  current  is  sent  out,  due  to  the  opening  and  closing  of  the  vibrat- 
ing armature  V.  The  exploring  coil,  Fig.  179,  is  then  moved  along  the  sur- 


198 


AMERICAN  TELEGRAPH  PRACTICE 


face  of  the  cable  sheath,  and  the  sound  due  to  induction  from  the  interrupted 
current  is  heard  in  the  receiver. 

When  the  point  is  reached  at  which  the  fault  exists,  the  sound  in  the 
receiver  will  cease  or  become  very  feeble.  If  now  the  coil  is  moved  still 
further  along  the  cable  sheath,  there  will  be  practically  no  sound,  while  on 
the  section  of  cable  between  the  fault  and  the  point  from  which  the  inter- 
rupted current  is  being  sent  out  there  will  be  a  pronounced  sound  in  the 


\ 


FIG.  178.—  Circuits  of  the  "Telafault." 

receiver.  This  enables  the  tester  to  locate  the  trouble  within  narrow  limits. 
The  exploring  coil  is  so  designed  that  by  proper  manipulation  all  return 
currents  in  the  sheath  of  the  cable  tending  to  interfere  with  exact  location  of 
the  fault  are  effectively  neutralized. 

In  small  cables,  having  100  conductors  or  under,  sometimes  it  is  possible 
to  remove  "  shorts"  and  "grounds"  without  opening  the  cable.  When  the 
trouble  has  been  located  at  a  definite  point,  if  the  cable  is  bent  back  and 
forth  several  times,  the  movement  of  the  conductors  thus  produced  fre- 
quently breaks  the  contact  and  clears  the  trouble. 

The  vibrator  should  be  ad- 
justed to  operate  at  about  600 
or  800  vibrations  per  minute. 
The  frequency  may  be  adjusted 
while  the  exploring  coil  is  held 
in  the  neighborhood  of  the 


FIG.  179. — Exploring  coil  of  the  Telafault. 


magnets  of  the  vibrator,  with  the  receiver  placed  to  the  ear.  The  tester 
should  familiarize  himself  with  the  particular  frequency  of  the  currents  sent 
out,  so  that  he  may  readily  recognize  the  testing  signal  when  the  exploring 
coil  is  held  close  to  the  sheath  of  the  cable  containing  the  conductors  being 
examined. 

The  external  connections  are  as  indicated  atA-B  Fig.  178.  For  locating 
grounds,  connect  A  with  the  cable  sheath  or  with  the  earth,  and  B  with  the 
faulty  conductor.  In  locating  crosses,  connect  the  ends  of  the  crossed  wires 
to  the  binding-posts  A  and  B.  In  all  cases  the  ends  of  the  wires  should  be  left 
open  at  a  point  beyond  the  trouble.  Then,  with  the  interrupter  in  operation, 
the  exploring  coil  is  moved  along  the  cable.  In  aerial  cable  measurements, 
tests  may  be  made  from  pole  to  pole  until  the  fault  is  located  between  two  cer- 


FA  ULT-FINDERS 


199 


tain  poles.  Then  if  the  messenger  wire  is  ridden  so  that  the  coil  may  be  applied 
directly  to  the  cable  sheath  along  the  span,  the  fault  may  be  located  within 
an  inch  or  so.  Usually  it  is  best  to  climb  only  every  third  or  fourth  pole 
until  the  trouble  is  located  within  narrow  limits,  thus  obviating  the  necessity 
of  climbing  every  pole  to  make  contacts.  Of  course,  where  a  Wheatstone 
bridge  set  is  available,  the  approximate  location  of  the  fault  should  be 
determined  by  means  of  the  Varley,  Fisher,  or  any  of  the  loop  tests,  after 
which  the  exploring  coil  may  be  employed  to  exactly  locate  the  point  at 
which  the  fault  exists. 

The  magnitude  of  the  sound  in  the  exploring  coil  depends  upon  the 
strength  of  the  field  produced  in  the  faulty  wire  by  the  interrupted  current, 
and  upon  the  intervening  distance  between  the  conductor  in  trouble  and 
the  lead  sheath. 

Should  the  pair  of  wires  in  trouble  be  in  the  center  of  a  large  cable,  the 
sound  in  the  receiver  due  to  induction  will  not  be  as  loud  as  if  they  were  lo- 
cated in  a  layer  near  the  surface.  An  average  case  would  be  where  the  con- 


1  2-  3. 

FIG.  180. — Various  positions  of  exploring  coil  on  sheath  of  cable. 

ductor  or  conductors  in  trouble  are  located  midway  between  the  sheath  and 
the  core  of  the  cable,  and  this  condition  with  the  regular  ten- volt  interrupter 
current  employed  permits  of  a  limiting  resistance,  for  grounds,  from  the  in- 
terrupter to  the  fault  and  return  of  100  ohms.  For  "shorts"  the  limiting 
resistance  is  about  500  ohms.  With  a  5o-volt  battery,  the  limiting  re- 
sistance, for  grounds,  is  600  ohms,  and  for  shorts  800  ohms,  or  thereabouts. 
The  Telafault  has  a  "heat  coil"  adjunct  which  automatically  opens  and 
closes  the  interrupter  circuit.  This  arrangement  permits  of  sending  out  a 
prearranged  series  of  impulses  at  regular  intervals,  and  which  may  be  readily 
distinguished  from  any  other  possible  induced  current  affecting  the  wires  in 
the  cable. 

In  attempting  to  locate  grounds  or  crosses  with  the  exploring  coil,  the 
coil  should  be  placed  on  the  sheath  as  indicated  in  position  i,  Fig.  180.  The 
spiral  lay  of  the  conductor  may  easily  be  followed  along  the  cable  by  means 
of  the  "tone."  This  insures  abrupt  cessation  of  the  sound  in  the  receiver 
when  the  fault  has  been  passed.  Position  2,  also,  may  be  used  for  the  same 


200 


AMERICAN  TELEGRAPH  PRACTICE 


purpose  as  position  i.  Position  3,  while  it  gives  the  greatest  volume  of 
sound  in  the  receiver,  should  not  be  used  after  the  fault  has  been  nearly 
located,  for  should  the  cable  sheath  or  the  conductor  be  grounded,  sound 
may  be  heard  beyond  the  fault. 

The  instrument  should  be  connected  at  a  cable  box  apparently  nearest 
the  trouble  in  order  to  reduce  resistance  to  fault.  In  case  of  wet  cable  or 
where  several  conductors  are  grounded  in  one  place,  as  many  conductors  as 
convenient  should  be  "bunched"  at  B,  Fig.  178. 

THE  WIRELESS  TROUBLE  FINDER 

There  are  several  different  makes  of  "wireless"  fault-finder,  among 
which  might  be  mentioned  that  manufactured  by  the  Electric  Specialty 


FIG.  181. — Queen  and  Co.'s  "wireless"  test  set. 

Company  of  Cedar  Rapids,  Iowa,  and  a  similar  instrument  manufactured 
by  Queen  &  Co.,  Philadelphia. 

The  former  is  extensively  employed  in  the  cable  testing  service  of  both 
telephone  and  telegraph  companies,  and  its  operation  is  practically  the 
same  as  that  of  the  "Telafault"  previously  described. 

In  using  the  wireless  tester  for  locating  faults,  a  working  conductor 
may  be  employed  as  one  side  of  the  testing  circuit  by  inserting  a  condenser 
in  series  with  the  working  conductor  used. 

Figure  181  is  a  photographic  reproduction  of  the  fault-finder  manufac- 
tured by  Messrs.  Queen  &  Co. 


CHAPTER  XI 
SPEED  OF  SIGNALING 

CIRCUIT  EFFICIENCY 

So  far  in  this  work,  the  only  method  of  telegraph  line  operation  con- 
sidered is  that  described  in  Chapter  VII,  dealing  with  single  Morse  trans- 
mission, by  means  of  which  one  message  is  sent  over  a  line  in  one  direction 
at  a  time. 

The  various  requirements  of  construction  and  of  operation  which  affect 
the  speed  of  signaling  constitute  the  factors  which  in  turn,  in  large  measure, 
determine  efficiency  of  circuit  operation. 

The  nature  of  the  service  is  such  that  line  wires  may  have  lengths  of 
from  a  few  hundred  feet  to  hundreds  of  miles,  and  in  view  of  what  was 
stated  in  the  preceding  chapter  in  regard  to  current  leakage  from  line  to 
ground,  where  aerial  lines  are  concerned,  it  is  apparent  that  the  longer  the 
line  the  greater  will  be  the  total  leak  in  a  particular  circuit. 

Obviously,  too,  the  longer  the  line,  the  greater  will  be  the  total  ohmic 
resistance  between  terminals,  and  the  greater  the  electrostatic  capacity 
of  the  circuit.  The  fact  that  increasing  the  length  of  the  line  involves 
increases  in  the  values  of  these  various  speed-limiting  factors  at  once  suggests 
that  there  are  fairly  well-defined  critical  lengths  of  line  which  can  be  operated 
at  a  satisfactory  degree  of  efficiency. 

Naturally  there  are  limitations  to  the  amount  of  voltage  which  may 
be  applied  to  a  wire.  For,  although  the  current  strengths  required  to  operate 
the  usual  type  of  receiving  instrument  are  of  small  volume,  the  compara- 
tively long  lengths  of  line  wire  stretching  between  stations  or  terminals 
constitute  resistances  which  in  themselves  greatly  reduce  the  current  which 
would  be  available  from  a  given  source  of  e.m.f.  on  shorter  circuits. 

Among  the  reasons  which  make  it  advisable  to  limit  the  applied  e.m.f. 
are,  first,  safety  of  employees  .handling  the  operating  instruments  and 
switching  apparatus;  second,  fire  risks  at  terminal  offices  where  battery  is 
applied  to  lines;  third,  the  deleterious  effects  of  electrostatic  induction 
between  neighboring  conductors  carrying  high  voltage;  fourth,  possible 
damage  to  instruments  and  apparatus  in  case  of  short  circuits,  or  in  case 
line  wires  become  grounded  near  the  terminal  station;  fifth,  destructive 
sparking  at  contact  points  of  "keys"  and  transmitters.  Also,  where  line 
wires  are  carried  through  aerial  or  underground  cables,  the  insulation  be- 
tween individual  conductors  carrying  high  voltages  is  constantly  subject  to 
break-down. 

201 


202  AMERICAN  TELEGRAPH  PRACTICE 

In  view  of  the  above  cited  considerations  it  is  obvious  that  it  is  not 
feasible  to  increase  the  length  of  satisfactorily  operative  circuits  simply  by 
applying  increased  battery  power. 

So  far  as  speed  of  signaling  is  concerned,  more  may  be  accomplished 
toward  increasing  the  efficiency  of  a  line  by  substituting  a  conductor  having 
higher  conductivity  per  unit  length,  and  by  bettering  the  insulation  obtaining 
throughout  the  length  of  the  circuit  between  line  and  ground.  Of  course, 
in  these  respects,  too,  there  are  imposed  limitations  which  concern  material 
and  dimension  of  conductor,  but  these  are  determined  by  what  is  commer- 
cially practicable. 

When  we  investigate  the  various  causes  which  make  it  advisable  in 
practice  to  divide  long  circuits  (say  from  New  York  to  San  Francisco) 
into  "repeater"  sections  of  approximately  500  miles,  we  learn  that  con- 
ductor resistance,  leakage  conductance,  conductor  capacity,  and  conductor 
inductance,  are  the  factors  which  limit  the  length  of  circuits  which  may  be 
operated  at  high  speed,  to  500  or  600  miles.  Theoretically,  the  most  satis- 
factory conditions  in  telegraph  circuits  obtain  when  the  conductor  resistance 
is  at  a  minimum,  when  leakage  conductance  is  low,  when  the  electrostatic 
capacity  of  the  line  is  lowest,  and  when  the  inductance  is  lowest. 

The  reader  here  is  referred  to  Chapter  VI  under  the  heading  "  Electro- 
static capacity  of  conducting  wires"  in  connection  with  Figs.  68  and  69, 
and  wherein  it  is  stated  that  electrostatic  capacity  has  the  same  effect  as 
if  it  retarded  or  delayed  the  initial  appearance  of  current  at  the  distant  end 
of  a  line.  And  further,  "  In  the  transmission  of  telegraph  signals  over  a  wire, 
the  circuit  is  closed  and  opened  four  or  five  times  per  second,  and  in  the 
case  of  long  lines,  the  effect  of  electrostatic  capacity  is  to  considerably 
curtail  the  number  of  impulses  or  signals  which  may  be  sent  over  the  wire 
in  a  given  length  of  time." 

If  the  line  wire  instead  of  being  suspended  30  or  40  ft.  above  the  earth 
were  suspended  but  a  few  inches  above  the  ground,  then,  due  to  the  reduced 
dimension  of  the  intervening  dielectric  (the  air)  between  the  wire  an^l  the 
ground,  the  electrostatic  flux  would  be  much  more  intense,  and  regardless 
of  other  factors,  there  would  be  a  marked  decrease  in  speed.' 

The  effect  of  electrostatic  capacity  in  reducing  the  number  of  impulses 
which  may  be  transmitted  over  a  wire  in  a  given  period  is  sometimes  referred 
to  as  retardation  and,  consequently,  as  the  electrostatic  capacity  increases, 
retardation  is  increased  proportionately.  The  impulse  impressed  on  the 
line  at  the  sending  end  is  required  to  charge  the  entire  surface  of  the  conductor 
before  it  can  affect  any  signaling  device  at  the  receiving  end  of  the  line. 
Furthermore,  when  the  circuit  is  opened  the  charge  accumulated  on  the  surface 
of  the  conductor  has  to  escape  or  be  withdrawn  from  it  before  the  signaling  in- 
strument at  the  receiving  end  releases  its  armature,  or  at  least  before  the  effects 
of  electrification  will  cease  to  be  in  evidence  at  the  receiving  end  of  the  line. 


SPEED  OF  SIGNALING 


203 


Thus  it  may  be  seen  that  there  is  an  advantage,  so  far  as  rapid  signaling 
is  concerned,  in  having  a  certain  amount  of  leakage  conductance  from  line  to 
earth,  provided  it  is  properly  distributed  along  the  length  of  the  line,  for, 
when  a  key  is  opened,  instead  of  having  to  wait  until  the  accumulated  charge 
travels  the  full  length  of  the  conductor  to  find  an  outlet,  the  distributed  leak- 
age paths  present  near-at-hand  avenues  of  escape  and  thus  " clear"  the  line  of 
the  charge  more  quickly.  The  objections  to  leakage,  however,  still  hold  good, 
and  a  critical  value  is  soon  reached  where  the  advantages  resulting  from  re- 
duced retardation  are  offset  by  the  consequent  reduction  in  current  volume 
in  the  coils  of  the  receiving  instrument,  which  follows  when  the  leakage  is 
excessive. 

The  truth  of  the  matter  is,  that  with  the  usual  standards  of  line  insula- 
tion maintained,  the  current  flow  in  a  line  is  never  wholly  interrupted.  This 
means  that  main-line  relays  whose  armatures  are  withdrawn  from  the  closed 
position  by  means  of  retractile  springs  are  so  adjusted  with  respect  to  "mark- 
ing" and  "spacing"  positions  of  the  armature  tongue  that  the  relay  operates 


FIG.  182. — The  effect  of  leakage  conductance  in  the  limiting  strength  of  operating 
and  releasing  currents. 

on  a  "margin"  of  current  strength,  somewhere  between  maximum  and  mini- 
mum current  flow.  Maximum  current  value  obtains  in  the  circuit  when  the 
keys  at  both  ends  of  the  circuit  are  closed,  and  minimum  value  when  either 
key  is  opened. 

Referring  to  Fig.  182 :  When  the  key  at  X  is  open,  the  strength  of  current 
traversing  the  coils  of  the  line  relay  at  Y  will  depend  upon  the  leakage  con- 
ductance of  the  combined  leakage  paths  to  earth  via  the  insulating  supports, 
and  other  avenues  of  escape  to  earth  along  the  length  of  the  line  toward  X . 
If  the  line  conductor  extending  between  X  and  Y  were  perfectly  insulated,  it 
is  evident  that  opening  the  key  at  X  would  completely  interrupt  the  current 
in  the  relay  at  Y,  but  the  fact  that  in  practice  there  is  a  certain  amount  of 
leakage  to  earth  means  that  when  the  key  at  X  is  opened,  the  battery  at  Y 
still  has  a  circuit  through  the  relay  at  Y  by  way  of  the  various  leakage 
paths  to  earth  and  back  to  the  other  terminal  of  the  battery  at  F. 


204  AMERICAN  TELEGRAPH  PRACTICE 

The  retractile  spring  adjustment  of  the  usual  type  of  single  main-line  relay 
and  of  the  "neutral"  (common  side)  relay  of  quadruplex  systems,  provides  a 
means  whereby  the  relay  may  be  made  to  release  its  armature  when  the  cur- 
rent traversing  the  relay  coils  has  fallen  in  strength  below  a  certain  value. 
Thus  we  realize  the  importance  of  high  insulation  resistance  of  line  wires, 
where  high  speeds  of  signaling  are  involved.  The  less  the  leakage  conductance, 
the  more  abrupt  will  be  the  cessation  of  current  in  the  relay  coils.  On  lines 
which  have  appreciable  leakage  the  opening  of  a  key  results  simply  in  reducing 
the  current  volume  flowing.  Practically,  this  means  that  the  retractile 
spring  attached  to  the  armature  of  the  relay  must  be  given  a  tension  which 
will  cause  it  to  withdraw  the  armature  when  the  current  strength  in  the  relay 
coils  has  fallen  below  a  certain  value,  and  which  will  be  overcome  when  the 
current  strength  has  increased  to  a  certain  value. 

To  illustrate:  suppose  that  the  maximum  current  strength  in  a  long  single 
Morse  circuit  is  75  milliamperes.  It  is  there  required  that  the  relay  arma- 
ture shall  be  attracted  when  the  current  has  built  up  to  a  strength  of  75  milli- 
amperes, and  average  leakage  conditions  impose  the  requirement  that  the 
armature  shall  be  released  when  the  current  has  fallen  to  a  value  of,  say,  20  or 
25  milliamperes.  This,  of  course,  is  taken  care  of  by  the  retractile  spring 
adjustment,  but  it  is  noteworthy  that  in  either  case  the  operation  of  the  relay 
in  reality  depends  upon  variations  in  current  strength,  and  not  as  it  would 
appear  theoretically,  upon  maximum  current  strength  and  upon  complete 
interruption  or  cessation  of  current  in  the  circuit. 

It  is  then,  apparent  that  the  " releasing"  current  will  have  a  greater 
strength  as  the  leakage  conductance  is  greater,  and — as  when  the  line  is  im- 
mersed in  a  heavy  fog,  or  when  the  insulation  resistance  of  the  line  has  been 
permitted  to  fall  to  a  low  value — the  length  of  circuit  which  may  be  satisfac- 
torily operated,  even  at  ordinary  hand  speeds,  will  be  diminished  accordingly. 

THE  EFFECT  OF  CABLED  CONDUCTORS  UPON  SPEED  OF  SIGNALING 

As  has  been  pointed  out,  the  effect  of  bringing  an  overhead  line  wire  into 
close  proximity  with  the  earth  (thus  increasing  the  electrostatic  capacity  of 
the  conductor)  results  in  increased  retardation.  Therefore  when  a  number  of 
conductors  are  insulated  and  made  up  in  the  form  of  a  cable,  a  condition  is 
created  practically  identical  with  that  which  exists  when  an  individual  con- 
ductor is  suspended  close  to  the  surface  of  the  earth.  That  is,  the  electrostatic 
capacity  of  each  conductor  in  the  cable  is  increased,  due  to  the  proximity  of 
neighboring  conductors.  This  is  true  whether  the  cable  is  suspended  at  the 
top  of  a  pole  line  40  ft.  above  the  earth,  or  whether  the  cable  is  buried  beneath 
the  surface  of  the  earth. 

At  the  outset  it  is  evident  that  telegraph  circuits  made  up  of  copper 
conductors  carried  in  cables  are  much  more  concerned  with  the  factors  of 
capacity  and  resistance  than  with  leakage  and  inductance.  A  cabled  con- 


SPEED  OF  SIGNALING  205 

ductor  is  continuously  supported  throughout  its  entire  length,  but  the  insula- 
tion resistance  of  the  support  is  practically  constant,  as  it  is  independent  of 
atmospheric  conditions.  It  is  true  that  tests  would  show  that  there  is 
measureable  leakage  conductance,  but  for  all  properly  constructed  cables 
the  leakage  is  not  sufficiently  appreciable  to  be  considered  as  a  factor  in 
limiting  the  receiving  end  current  volume. 

As  was  stated  in  a  previous  chapter  (page  124)  the  presence  of  inductance 
in  a  circuit  tends  to  choke  currents  which  alternate  in  polarity.  The  presence 
of  inductance  in  a  circuit  also  has  a  retarding  effect  upon  direct  currents  when 
initially  applied.  When  a  telegraph  circuit  which  is  operated  from  a  source 
of  direct  current  is  opened  or  closed,  that  is,  while  the  current  in  the  circuit 
is  diminishing  or  increasing,  the  presence  of  inductance  in  the  first  case  has 
the  effect  of  prolonging  the  current,  and  in  the  second  case  has  the  effect  of 
delaying  the  increase  of  current  strength  in  the  circuit. 

Elsewhere  it  has  been  stated  that  when  a  circuit  carrying  current  is  closed 
(completed)  a  magnetic  field  is  established  about  the  conductor,  which, 
as  long  as  the  circuit  remains  closed,  may  be  regarded  as  stored  about  the 
conducting  wire.  The  presence  of  inductance  in  a  circuit  is  manifested  by 
the  appearance  of  a  bright  bluish  spark  at  contact  points  due  to  the  so-called 
extra  current  when  the  circuit  is  opened.  The  spark  represents  the  stored 
energy  of  the  magnetic  field,  which  produces  a  direct  current  at  the  instant 
the  circuit  is  opened.  When  the  circuit  is  "made"  or  closed,  there  is  no 
spark  produced  at  the  contact  points  of  the  key  due  to  self-induction  as 
the  extra  current  is  then  in  an  inverse  direction,  and  is  engaged  in  the  work 
of  storing  energy  around  the  conductor  in  a  direction  proceeding  away  from 
the  point  where  the  charging  current  is  applied  to  the  wire. 

A  formula  applicable  to  direct  currents,  for  determining  the  current 
value  of  the  energy  stored  in  the  magnetic  field  surrounding  the  conductor, 
and  which  has  long  been  the  basis  .of  such  calculations,  is  1/2  LI2,  in  which 
L  represents  inductance  in  henries,  and  /  the  current  in  amperes.  This  is 
apparent  from  the  fact  that  while  the  magnetic  field  gradually  increases  to 

LI  lines,  the  mean  value  of  the  current  would  be  — . 

Helmholtz'  law  (page  95)  in  its  application  to  telegraph  transmission 
problems  points  to  the  conclusion  that  where  the  inductance  is  small  as 
compared  with  the  ohmic  resistance  of  the  circuit,  the  amount  of  retardation 
chargeable  to  inductance  is  inappreciable. 

With  leakage  and  inductance  eliminated  as  important  factors,  there  are 
left,  so  far  as  cabled  conductors  are  concerned,  the  factors  capacity  and 
resistance. 

THE  KR  LAW 

The  constantly  increasing  amount  of  aerial  and  underground  cable  which 
is  taking  the  place  of  open-pole  line  construction  means  that  more  or  less 


206  AMERICAN  TELEGRAPH  PRACTICE 

extensive  sections  of  trunk  lines  pass  through  cables,  and  this  results  in 
placing  overland  circuits  in  the  category  of  cable  circuits,  at  least  through 
those  sections  where  overland  wires  are  carried  through  cables. 

In  cable  operation  it  is  understood  that  the  time  required  to  transmit  a 
given  number  of  impulses  varies  almost  in  direct  proportion  to  the  capacity 
and  the  resistance  of  the  conductor,  which  in  any  given  case  would  give  a 
quantity  KR.  And,  as  in  most  cases  capacity  and  resistance  are  proportional 
to  the  length  of  the  cable,  it  is  evident  that  the  resulting  retardation  is  pro- 
portional to  the  square  of  the  length  of  the  cable.  Suppose,  for  example 
that  it  is  desired  to  ascertain  the  value  of  the  quantity  KR  in  a  cable  con- 
ductor 100  miles  long  having  a  resistance  of  20  ohms  per  mile  and  a 
capacity  of  0.3  m.f.  per  mile,  then 

(20  X  i oo)X  (0.3X100)  =60,000,   the   KR  of  the   circuit. 

In  this  connection  it  is  interesting  to  note  the  KR  value  of  an  overhead 
line  suspended  in  the  usual  manner  upon  insulators.  A  No.  9  copper  wire, 
for  instance,  with  a  resistance  of  4  175  ohms  per  mile,  and  a  capacity  of 
approximately  0.012  m.f.  per  mile,  would  have,  for  a  loo-mile  line,  a  KR  of 

(o.oi2Xioo)X(4  1/5X100)  =  504. 

For  the  purpose  of  emphasizing  the  relation  which  the  quantity  KR  in 
cabled  conductors  has  to  transmission  efficiency,  we  might  consider  the  effects 
produced  by  it  in  cables  used  for  telephonic  purposes,  where  practically  all 
of  the  transmission  losses  experienced  are  attributed  to  that  quantity. 

In  one  of  his  electrical  papers  John  B.  Adams  states  that  the  transmission 
loss  may  be  regarded  as  being  proportional  to  the  square  root  of  the  product 
obtained  by  multiplying  the  resistance  of  the  completed  circuit  by  the  mutual 
capacity  of  the  circuit  in  farads,  or 

Loss  in  transmission  =  7£  v  7?XC 

in  which  R  represents  the  loop  resistance  in  ohms, 

C  the  mutual  capacity  in  farads, 
and  K  a  constant  approximately  equal  to  the 
average  frequency  of  voice  currents. 

The  application  of  this  formula  in  comparing  the  relative  transmission 
losses  of  conductors  of  different  gages  (where  metallic  circuits  and  mutual 
capacity  are  involved)  indicates  that  the  loss  in  transmission  is  not  directly 
proportional  to  the  KR  of  the  circuit.  In  the  operation  of  telegraph  lines, 
where  grounded  circuits  generally  are  employed,  and  where  the  form  of  ca- 
pacity encountered  is  somewhat  different  from  that  considered  in  the  above 
formula,  the  quantity  KR  may  safely  be  taken  as  the  criterion  of  the  speed 
of  signaling  through  cables. 


SPEED  OF  SIGNALING  207 

•  Measurements  made  on  rubber-insulated  and  on  paper-insulated  cables 
used  in  telegraph  service  show  an  average  capacity  per  mile  per  conductor 
for  rubber  covered  0.62  m.f.  and  for  paper  o.io  m.f. 

A  cabled  conductor  of  No.  14  gage  when  rubber  covered  for  a  length  of 
i  mile  is  as  detrimental  to  telegraph  transmission  as  a  length  of  2  1/2  miles 
of  paper-insulated  conductor  of  the  same  gage.  And  in  general,  for  any 
length  of  conductor  the  loss  is  proportionate  with  length. 

A  No.  9  copper  wire  weighing  210  Ib.  per  mile,  suspended  on  poles  and 
having  a  capacity  to  ground  of  0.012  m.f.  per  mile  for  a  line  length  of  130 
miles  would  have  a  telegraph  transmission,  efficiency  equivalent  to  i  mile  of 
rubber-covered  cabled  conductor. 


TELEGRAPH    SPEED    IN   WORDS   PER   MINUTE 

With  reference  to  the  number  of  words  that  can  be  transmitted  over 
a  given  line  in  a  given  time,  the  speed  of  signaling  depends  considerably 
upon  the  methods  of  transmission  employed.  If  signals  were  transmitted 
by  regularly  periodic  pulsations,  or  by  alternations  of  current  continuously 
impressed  upon  the  line,  the  transmitting  apparatus  could  be  designed  to 
meet  the  transmission  efficiency  of  the  circuit,  as  in  the  case  of  alternating- 
current  lighting  and  power  operations. 

It  is  well  known  that  hand  transmission  is  quite  inefficient,  and  the  num- 
ber of  words  per  minute  that  can  be  sent  over  a  given  line  varies  with  differ- 
ent operators — this,  aside  from  the  relative  skill  of  different  operators 
in  rapidly  manipulating  the  sending  key.  A  certain  operator,  for  instance, 
may  be  capable  of  sending  40  wrords  per  minute  over  a  short  line  (where  the 
total  insulation  of  the  line  is  high,  and  where  the  variations  in  operating  and 
releasing  currents  are  a  maximum)  while  on  a  long  circuit  he  may  find  it 
necessary  to  slow  down  his  speed  to,  say,  20  words  per  minute  in  order 
properly  to  actuate  the  receiving  relay  at  the  other  end  of  the  line.  Another 
operator,  who  can  transmit  but  30  words  per  minute  over  the  short  line, 
may  be  able  to  keep  up  this  same  speed  over  the  long  circuit,  and  still  have 
his  signals  reach  the  receiving  end  firm  and  strong. 

This  brings  to  notice  the  fact  that  hand  transmission  is  irregular;  meaning 
that  the  transmission  capabilities  of  the  circuit  are  not  always  availed  of  to 
the  fullest  extent.  The  difficulty  ;s  that  in  many  cases  the  duration  of  con- 
tact is  not  long  enough.  The  "  dot "  elements  of  the  letters  may  be  made  too 
rapidly,  and  signaling  time  may  be  lost  in  unnecessarily  long  spacing.  These 
inaccuracies  of  transmission  are  peculiar  to  hand  sending,  and  in  large 
measure  are  obviated  by  machine  transmission,  such  as  that  employed  in 
Wheatstone  operation. 

The  Morse  alphabet  consisting  of  26  English  letters  is  made  up  of  "dots" 
" dashes"  and  spaces.  The  basis  of  the  alphabet  is  the  dot.  A  dash  is 


208  AMERICAN  TELEGRAPH  PRACTICE 

equivalent  in  length  to  three  dots.  The  space  between  the  elements  of  a 
letter  is  equal  to  one  dot.  The  space  between  the  letters  of  a  word  is  equal 
to  three  dots,  and  the  spaces  between  any  two  words  is  equal  to  six  dots. 

The  American  Morse  alphabet  (26  letters)  has  a  total  of  77  elements, 
with  an  average  for  each  letter  of  2.9615  elements;  or  for  a  five-letter  word 
an  average  of  14.807  elements. 

The  Continental  Morse  alphabet  (26  letters)  has  a  total  of  82  elements, 
or  3.1538  average  signals  per  letter,  and  15.769  average  signals  per  average 
word  of  five  letters. 

Including  spaces,  the  average  five-letter  word  (American  Morse)  con- 
tains 36.59  dot  elements,  or  practically  5  per  cent,  less  than  a  five-letter 
word  composed  of  Continental  signals.  A  sending  speed  of  25  words  per 
minute  means  394.22  signals  per  minute  in  the  case  of  the  European  alphabet, 
and  370.17  signals  per  minute  in  the  case  of  the  American  Morse.  The 
last  two  estimates  are  exclusive  of  space  elements  between  words.  All  of 
the  above  figures  are  obtained  by  simple  multiplication,  and  are  based  on 
lengths  of  dot,  dash,  and  space  agreeing  with  the  scientific  arrangement  of 
the  alphabet. 

With  manual  transmission  it  is  found  that  length  of  dot,  dash,  and  space 
does  not  accurately  agree  with  that  intended,  the  result  of  which  is  that  a 
considerable  amount  of  signaling  time  is  lost  in  unduly  prolonged  spacing, 
and  this  constitutes  so  much  dead  time.  When  it  is  shown  that  the  calcu- 
lated number  of  words  per  minute  have  been  handled  in  a  given  instance,  it 
means  simply,  that  the  extra  time  consumed  in  spacing  has  been  used  up 
at  the  expense  of  the  signaling  elements — that  their  duration  of  contact 
has  been  cut  short. 

SEMI-AUTOMATIC  TRANSMITTERS 

Within  recent  years  semi-automatic  sending  machines  in  various  forms 
have  been  extensively  introduced.  One  of  these  machines  the  Yetman,  is 
operated  by  means  of  a  type-writer  keyboard,  and  is  designed  to  transmit 
perfectly  formed  Morse  characters,  provided  the  contact  disks  are  kept 
clean.  If  these  disks  are  permitted  to  accumulate  dirt,  or  foreign  matter 
of  any  kind,  or  to  become  rough  or  uneven  of  surface,  the  transmitted  signals 
may  be  "light"  owing  to  the  introduction  of  high  resistance,  or  to  drop  out 
entirely  owing  to  failure  of  contact.  This  machine  is  operated  in  the  same 
way  as  an  ordinary  type-writer,  simply  by  depressing  the  type  key  of  the 
letter  it  is  desired  to  transmit.  Intelligent  operation  and  good  judgment  are 
required,  however,  in  order  to  effect  even  continuous  transmission,  as  it  is 
evident  that  a  letter  "B"  (dash  and  three  dots)  should  be  given  a  longer 
time  to  form  than  a  letter  "E"  (one  dot). 

The  various  transmitters  of  the  Mecograph,  Vibroplex  type,  in  forming 


SPEED  OF  SIGNALING  209 

dashes  require  as  many  movements  of  the  hand  as  are  required  with  the 
ordinary  Morse  key,  while  any  required  number  of  dots  are  made  by 
holding  the  lever  on  one  side,  allowing  the  lever  to  vibrate  and  thus  re- 
gularly close  and  open  the  main-line  circuit  until  the  desired  number  of 
dots  have  been  formed. 

It  may  be  that  a  semi-automatic  transmitter  can  be  developed  which 
will  meet  the  needs  more  satisfactorily  than  any  so  far  introduced,  for  al- 
though the  sending  machines  at  present  in  use  have  surely  made  for  increased 
speed  of  signaling,  they  have,  in  many  instances,  been  the  cause  of  poorly 
founded  reflections  being  cast  upon  the  electrical  efficiency  of  a  certain  class 
of  circuits. 

The  difficulty  is  that  automatic  sending  devices  frequently  are  so  adjusted 
that  the  dot  portions  of  the  letters  are  made  at  a  rate  of  50  to  90  words  per 
minute,  while  the  actual  speed  in  words  per  minute  attained  by  the  operator 
may  amount  to  less  than  30.  This  being  the  case,  there  exists  in  a  more 
aggravated  form,  the  same  loss  in  signaling  time  on  account  of  undue  pro- 
longation of  the  spacing  elements,  with  the  added  defect  that  the  dots  are 
more  "clippy"  and  the  duration  of  the  dot  contact  more  transitory  and 
fleeting. 

It  is  plain,  then,  that  when  a  circuit  has  been  designed  to  have  a  certain 
efficiency,  whether  or  not  that  efficiency  is  attained  depends  greatly  upon 
the  character  of  transmission  employed  in  its  operation. 

SPEED  OF  SIGNALING  OVER  OPEN  AERIAL  LINES 

The  fact  that  most  main  telegraph  offices  are  located  in  the  heart  of 
the  business  section  of  towns  and  cities  means  that  most  of  the  long  trunk 
circuits,  in  the  aggregate,  pass  through  a  considerable  amount  of  underground 
cable,  as  modern  conditions  are  such  that  electric  wires  are  required  to  be 
placed  underground  in  cities  of  any  considerable  size.  Circuits  between 
New  York  and  Chicago  (1,000  miles)  pass  through  from  20  to  50  miles  of 
cable,  depending  upon  the  route  taken.  As  the  tendency  is  to  increase  the 
amount  of  underground  cable  used,  most  long-distance  circuits  have  to  be 
regarded  as  made  up  of  part  underground  and  part  aerial  line,  and  any 
question  of  circuit  efficiency  must  take  into  consideration  the  factors  obtain- 
ing in  each  form  of  construction.  In  any  given  case,  the  great  preponderance 
of  open  aerial  conductor  over  that  placed  underground  permits  of  covering 
much  greater  distances  than  if  the  circuit  throughout  its  entire  length  were 
contained  in  a  cable.  Where  overhead  open  lines  are  concerned,  the  factor 
of  leakage  enters  as  a  most  important  consideration,  and  the  KR  law  no 
longer  holds  good  as  the  only  quantity  or  factor  involved. 

"CROSS-FIRE" 

Another  disturbing  factor  which  must  be  taken  into  consideration  is 
that  variously  referred  to  as  "cross-fire,"  "transverse  leakage,"  "weather- 

14 


210  AMERICAN  TELEGRAPH  PRACTICE 

cross,"  etc.,  and  it  may  well  be  taken  into  account  here,  as  its  effects  upon 
the  circuit  efficiency  of  open  aerial  lines  are  of  no  less  importance  than  is 
that  of  leakage  conductance  to  earth. 

During  damp  or  rainy  weather,  when  insulators  are  covered  with  a 
heavy  film  of  moisture,  and  when  cross-arms,  pins  and  poles  are  water- 
soaked,  there  is  an  intermingling  of  currents  between  the  various  wires  on  a 
pole  line. 

On  pole  lines  where  there  are  a  number  of  wires  it  is  usually  the  case 
that  some  of  the  circuits  are  being  operated  with  current  strengths  consider- 
ably in  excess  of  that  obtaining  in  other  circuits  on  the  same  poles,  and  the 
tendency  is  for  the  stronger  currents  to  leak  into  the  shorter  circuits  of 
lower  resistance.  Also,  there  are  periods  in  the  operation  of  all  circuits 
when  for  an  instant  (constantly  recurring)  the  regular  battery  is  removed 
from  the  line.  During  these  brief  intervals  in  the  operation  of  a  given 
circuit  it  happens  that  full-current  strength  is  impressed  upon  adjacent 
circuits  and  the  tendency  is  for  these  currents  to  leak  through  the  weather- 
bound supports  into  the  lines  temporarily  without  battery  of  their  own, 
and  thus  create  cross-fire,  or  weather-cross  between  the  two  neighboring 
circuits.  In  those  instances  where  unfavorable  weather  conditions  extend 
over  any  considerable  length  of  line,  the  effects  produced  seriously  interfere 
with  the  efficient  operation  of  circuits.  In  some  cases  false  signals  are 
produced  in  receiving  relays  due  to  their  being  actuated  by  transverse 
leakage  currents  from  neighboring  wires. 

Cross-fire  disturbances  are  sometimes  attributed  to  induction,  but 
this  conception  of  the  difficulty  is  in  error,  as  the  effects  produced  are  more 
pronounced  during  the  prevalence  of  wet  weather  and  should  not  be 
confused  with  the  effects  attributable  to  electrostatic  or  electromagnetic 
induction. 

The  weather-cross  may  be  regarded  more  in  the  nature  of  a  high  resistance 
contact  between  adjacent  conductors. 

Due  to  variations  in  temperature,  to  alteration  in  the  value  of  total 
leakage  conductance,  on  long  aerial  lines  the  conductivity  of  wires  not 
infrequently  changes  as  much  as  10  per  cent.,  sometimes  within  a  few  minutes. 
This  makes  it  difficult  to  develop  working  formulae  which  accurately  disclose 
the  true  conditions  to  be  dealt  with.  Certainly  it  is  not  practicable,  nor 
would  it  be  safe  to  be  governed  by  formulae  (such  as  that  of  the  KR  law) 
which  deal  with  definite  and  constant  quantities. 

In  the  very  thorough  and  comprehensive  investigations  conducted  by 
Mr.  F.  F.  Fowle,  into  the  problems  of  telegraph  transmission,  in  which  he 
starts  out  as  a  basis  with  the  well-known  differential  equation  covering 
the  full  solution  of  transmission  problems  of  any  character^ 


SPEED  OF  SIGNALING 


211 


in  which  E  =  line  potential. 

5  =  distance  from  source. 
/  =  time. 

r  =  line  resistance. 
g  =  leakage  conductance. 
C  =  line  capacity. 

inductance. 


And  proceeding  upon  the  theory  that  for  overhead  circuits  the  only  practic- 
able basis  of  determining  circuit  efficiency  is  that  having  to  do  with  strength 
of  received  signals,  which  permits  of  the  elimination  of  the  time  element, 
the  equation  resolves  into 

d2E 


The  general  solution  of  which  and  the  deductions  made  therefrom  led  Mr. 
Fowle  to  compile  the  table  shown  herewith,  which  gives  the  maximum  per- 
missable  length  of  line  which  may  be  operated  satisfactorily,  either  simplex, 
duplex,  or  full  quadruplex,  over  a  wire  of  given  resistance  per  mile. 


Conductor  resistance 
per  mile 

Maximum  permissable  length  of  line 

Simplex 

Duplex 

Quadruplex 

2  ohms  

597  miles 
510  miles 
450  miles 
376  miles 
331  miles 
299  miles 
248  miles 
217  miles 

783  miles 
658  miles 
580  miles 
485  miles 
425  miles 
384  miles 
318  miles 
278  miles 

531  miles 
442  miles 
386  miles 
313  miles 
268  miles 
236  miles 
1  86  miles 
156  miles 

3  ohms.. 

4  ohms  
6  ohms.. 

8  ohms.. 

10  ohms  

15  ohms.. 

20  ohms.. 

In  each  case  an  insulation  resistance  of  0.25  megohm  per  mile  was  used 
in  the  investigations  from  which  the  above  figures  were  determined. 

For  the  simple  Morse  or  simplex  circuits  a  terminal  resistance  of  300  ohms 
was  employed.  Relays  having  a  resistance  of  150  ohms,  adjusted  to  operate 
on  0.060  ampere,  and  release  on  0.045  ampere,  were  used  in  the  tests. 

The  figures  submitted  for  duplex  operation  assume  the  employment  of 
polar  relays  having  a  total  resistance  of  800  ohms,  and  an  internal  battery 
resistance  of  300  ohms.  The  relay  current  was  0.030  ampere.  The  quad- 
ruplex figures  are  based  on  the  employment  of  4oo-ohm  polar  relays,  8oo-ohm 


212  AMERICAN  TELEGRAPH  PRACTICE 

neutral  relays,  and  6oo-ohm  internal  battery  resistance.  The  "  short  end  " 
potential  used  was  90  volts,  and  the  "long  end"  315  volts. 

In  comparing  the  values  obtained  by  means  of  the  "leakage"  theory, 
with  those  which  the  KR  law  would  give,  Mr.  Fowle  points  out  that  in  a 
given  case  where  a  No.  9  copper  conductor  is  employed  for  telegraph  trans- 
mission, the  leakage  theory  indicates  a  maximum  operative  limit  of  314  miles, 
while  the  KR  law  would  indicate  a  maximum  operative  limit  of  487  miles. 

For  an  iron  wire  of  approximately  No.  8  gage,  the  leakage  theory  gives  ah 
operative  limit  of  258  miles,  while  the  KR  law  'ndicates  that  the  limit  of 
satisfactory  operation  would  be  291  miles. 

In  calculations  dealing  with  circuit  efficiency,  it  should  be  kept  in  mind 
that  in  addition  to  the  line-conductor  properties — resistance,  capacity  and 
leakage  conductance — the  resistance  and  inductance  of  the  terminal  appa- 
ratus (including  relays  and  protective  devices)  must  be  treated  as  important 
factors  having  a  bearing  on  the  properties  of  the  circuit  as  a  whole. 

In  considering  the  question  of  speed  (in  words  per  minute)  it  is  elucidative 
to  regard  the  speed  of  the  receiving  apparatus  separately  from  the  speed  of 
the  line. 

While  it  is  true  that  the  design  of  a  satisfactory  receiving  relay  for  high- 
speed work  is  hedged  about  with  many  requirements,  it  is  generally  under- 
stood that  the  "speed"  of  a  line  of  average  length,  in  good  physical  and 
electrical  condition,  is  considerably  above  the  operating  speed  of  the  usual 
electromagnetic  types  of  receiver  employed.  It  is  probable  that  in  many 
cases  "  4oo-word-per-minute  "  lines  are  equipped  at  the  terminals  with  "100- 
word-per-minute"  apparatus.  On  the  other  hand  it  sometimes  happens 
that  the  opposite  condition  prevails. 

In  order  to  reconcile  these  discrepancies,  and  with  the  object  of  developing 
a  "theory"  applicable  in  all  cases,  several  investigators1  have  suggested 
that  the  theory  of  alternating-current  transmission  can  safely  be  extended  to 
include  the  case  of  signaling  over  aerial  lines  and  through  cables. 

The  application  of  this  theory  requires  that  the  relative  frequency  of  dot 
and  dash  signaling  compared  with  the  frequency  of  simple  dot  signaling,  be 
determined.  This  consists  in  finding  the  receiving  end  impedance  of  the  cir- 
cuit, including  that  of  the  receiving  instruments,  and  considering  the  value 
of  the  impressed  e.m.f.  at  the  transmitting  end.  In  practice  it  is  apparent 
that  the  impedance  of  the  receiving  apparatus  has  a  decided  influence  upon 
the  amplitude  of  the  received  impulses,  and  constitutes  a  factor  that  must  be 
reckoned  with. 

From  an  alternating-current  standpoint,  the  receiving  end  impedance  is 
the  true  criterion  of  speed  in  any  signaling  circuit ;  that  is,  for  given  limits  of 
sending  voltage,  and  for  given  sensibility  of  receiving  instrument.  Its 
application  to  everyday  telegraph  requirements,  however,  is  not  likely  to 

1  Dr.  Kennelly,  Bela-Gati,  Hockin,  S.  R.  Beatty  and  others. 


SPEED  OF  SIGNALING  213 

meet  with  general  favor,  on  account  of  the  calculation  involved.  It  is  appar- 
ent also  that  the  information  obtainable  by  that  method,  would  be  no  more 
exact,  nor  would  it  be  as  susceptible  of  simple  and  rapid  application,  as  is 
the  leakage  theory,  which  requires  only  tabulated  data  showing  requisite 
received  current  strengths. 

The  inductance  possessed  by  a  relay  or  other  electromagnetic  receiving 
instrument  is  largely  dependent  upon  the  efficiency  of  the  magnetic  circuit 
of  the  instrument. 

The  magnetic  circuit  of  a  relay  consists  of  the  iron  cores  of  the  magnets, 
the  iron  "heel"  piece  or  yoke  joining  the  cores,  and  the  movable  iron  armature 
mounted  in  front  of  the  magnets  (see  Fig.  88).  The  more  perfect  the  mag- 
netic circuit,  the  greater  will  be  the  inductance  of  the  electrical  circuit  which 
includes  the  windings  of  the  magnets  as  a  portion  thereof.  Should  the  mov- 
able iron  armature  be  permitted  to  come  into  actual  contact  with  the  iron 
cores  of  the  coils,  the  magnetic  circuit  will  be  complete,  and  the  self-induction 
of  the  magnets  will  be  a  maximum.  If  on  the  other  hand  the  armature  is  so 
regulated  in  its  forward  travel  that  it  "is  stopped  by  the  "closed  contact" 
adjusting-screw  before  coming  into  contact  with  the  pole-faces,  the  magnetic 
circuit  will  not  at  any  time  be  complete,  and  as  a  consequence  the  self- 
induction,  or  inductance  of  the  magnets  will  be  less  than  if  the  magnetic 
circuit  were  "complete"  as  above  explained. 

For  telegraphic  purposes  it  is  not  always  necessary  that  the  magnetic 
circuit  of  the  receiving  instrument  should  be  efficient.  In  other  words  there 
are  times  (for  instance,  where  high-speed  work  is  concerned)  when  it  is  of 
considerable  advantage  to  sacrifice  magnetic  efficiency.  Especially  is  this 
true  when  by  doing  so  the  inductance  of  the  instrument  may  be  reduced. 

We  have  before  us  now  the  question  of  "receiving  end  impedance"  as 
having  a  bearing  upon  the  speed  of  signaling.  By  referring  to  Chapter  6, 
under  the  heading  "Electromagnetic  Induction,"  we  find  that  the  resistance 
in  ohms  combined  with  the  inductance  in  henries  produces  the  property 
known  as  impedance,  and  by  again  reviewing  that  portion  of  the  work,  also 
the  section  under  the  heading  "Time-constant"  it  may  be  learned  that  the 
inductance  of  the  coils  of  the  receiving  instrument  constitutes  a  very  decisive 
factor  in  determining  the  "speed"  of  the  circuit  as  a  whole. 

These  various  considerations  suggest  that  great  caution  should  be  exer- 
cised in  collating  the  factors  involved  in  "speed"  formulae. 

It  is  manifestly  insufficient  to  consider  only  the  line  factors  without  regard 
to  the  speed  capabilities  of  the  receiving  apparatus.  It  is  quite  possible  that 
in  the  average  investigation  considerable  time  and  expense  might  be  devoted 
to  making  the  speed  capabilities  of  the  line  or  of  the  instrument  higher  than 
they  need  be.  Of  course,  it  is  good  practice  to  have  reliable  margins  above 
the  requirements  in  either  case,  but  it  is  obvious  that  expense  involved  in 
making  a  line  fifty  per  cent,  faster  than  the  available  receiving  instrument,  is 


214 


AMERICAN  TELEGRAPH  PRACTICE 


not  justifiable.  If  the  conditions  are  the  reverse,  excessive  expense  in  mak- 
ing the  receiving  instrument  unnecessarily  faster  than  is  the  available  circuit, 
is  not  justified. 


RELAY  CHARACTERISTICS 


In  practice  it  is  found  that  the  design  and  construction  of  relays  as  well 
as  the  different  products  of  various  manufacturers  has  considerable  to  do 
with  the  speed  capabilities  of  these  receiving  instruments. 

Tests  made  with  five  polar  relays  procured  from  five  different  sources,  gave 
the  following  values: 


Winding 

Resistance, 
ohms 

Inductance, 
henries 

1,000  turns,  single  silk-covered,.  3  i-gage  wire, 

each 

1  08 

1.88 

section. 

1,000  turns,  single  silk-covered,  3i-gage  wire, 

each 

ic8 

2.76 

section. 

1,400  turns,  single  silk-covered,  32-gage  wire, 

each 

193 

3-039 

section. 

i,  600  turns,  single  silk-covered,  32-gage  wire, 

each 

270 

3.921 

section. 

1,400  turns,  single  silk-covered,  34-gage  wire, 

each 

300 

5-99 

section. 

The  tests  were  made  with  13  milliamperes  current,  and  20  mils  air-gap  be- 
tween armature  and  pole-faces  of  magnets. 

L 

Applying  the  formula  for  determining  the  time-constant  in  seconds 


in  the  case  of  each  relay  here  considered,  it  may  be  shown  that  in  the  order 
given,  the  respective  values  are: 

0.017  second, 
0.025  second, 
0.015  second, 
0.015  second, 
0.019  second, 

from  which  it  would  appear  that  relays  Nos.  3  and  4  should  operate  at  greater 
speeds  than  the  others.  Also  that  relay  No.  i  would  be  next  fastest,  and  then 
No.  5  and  No.  2  respectively.  But  these  figures  apply  theoretically  only,  as 
they  divulge  simply  the  functional  performance  of  the  magnetic  circuit  with- 
out regard  to  the  operation  of  the  moving  element  (the  armature)  of  the 
relay.  Actual  speed  tests  made  with  the  particular  relays  above  consid- 
ered showed  that  relay  No.  i  when  operated  on  3-m.a.  current  failed  to 


SPEED  OF  SIGNALING  215 

record  signals  intelligibly,  operated  at  a  speed  of  30  words  per  minute.  When 
the  current  strength  was  raised  to  10  m.a.  the  signals  at  30  words  per  minute 
were  perfect. 

Relay  No.  2  performed  practically  the  same  as  No.  i. 

Relay  No.  3  operated  on  3-m.a.  current,  recorded  perfectly;  signals  trans- 
mitted at  the  rate  of  30  words  per  minute. 

Relay  No.  4  performed  practically  the  same  as  No.  3. 

Relay  No.  5  performed  practically  the  same  as  Nos.  i  and  2. 

The  results,  therefore,  were  not  what  the  time-constant  considered  alone 
would  have  foretold,  as  theoretically  the  difference  in  performance  between 
relays  i  and  2  should  have  been  more  pronounced. 

Of  course,  in  each  of  the  tests,  when  the  current  strength  in  the  relay 
circuit  was  raised  to  average  operating  value,  say  25  m.a.,  the  speed  possi- 
bilities of  each  relay  were  very  greatly  increased.  In  the  case  of  polar  relay 
No.  3,  for  instance,  having  a  time-constant  of  0.015  second,  it  is  evident  that  if 
the  armature  in  its  movements  forward  and  backward  faithfully  followed  the 
current  reversals  in  the  magnet  coils,  it  would  make  33  1/3  excursions  over 
and  back  per  second,  which  on  the  basis  of  15  excursions  per  average  word 
would  signify  a  speed  of  133  1/3  words  per  minute. 

The  extra  time  consumed  in  forming  the  dash  elements  of  the  letters, 
naturally  would  curtail  the  number  of  current  reversals  the  relay  would  be 
called  upon  to  receive  in  a  given  length  of  time,  and  this  would  reduce  some- 
what the  number  of  words  per  minute  transmitted  by  means  of  the  dot  and 
dash  code. 

FIGURE  OF  MERIT 

A  number  of  relays  having  identical  values  of  inductance  and  resistance 
when  tested  for  the  purpose  of  ascertaining  the  least  amount  of  current 
required  to  operate  them;  generally  will  be  found  to  vary  more  or  kss  in  this 
respect.  The  instrument  which  operates  satisfactorily  with  the  least  current 
strength  has  the  lowest  figure  of  merit.  If  in  a  given  case  a  relay  is  found 
to  operate'  satisfactorily  on  0.002  ampere,  the  figure  of  merit  of  that  relay 
is  2  milliamperes. 

RELAY  ARMATURE   SUPENSION 

With  the  current  requirements  of  the  receiving  relay  well  understood,  there 
remain  as  factors  susceptible  of  alteration,  and  possibly  of  improvement,  the 
suspension  of  the  armature  and  the  arrangement  of  the  magnetic  circuit. 

Fleeming  Jenkin,  in  his  book  on  "  Electricity  and  Magnetism,"  aptly 
states  the  case  in  regard  to  the  relay  armature  thus: 

"The  mass  of  the  armature  should  be  so  distributed  that  its  moment  of  inertia 
may  be  the  smallest  that  is  consistent  with  the  necessary  weight  of  the  armature  and 
position  of  the  pivots;  any  increase  in  the  moment  of  inertia  produces  a  propor- 
tional diminution  in  the  angular  velocity  with  which  the  tongue  will  move  under  a 


216  AMERICAN  TELEGRAPH  PRACTICE 

given  force,  and  the  rate  at  which  a  relay  will  work  depends  upon  this  angular 
velocity.  If  the  moment  of  inertia  be  doubled,  the  force  remaining  the  same,  the 
angular  velocity  acquired  in  a  given  time  will  be  halved,  but  to  traverse  the  same 
angle;  i.e.,  to  traverse  the  space  between  one  contact  and  the  other,  will  not  require 
double  the  time,  but  only  1.414  times  the  period  required  by  the  lighter  armature, 
because  1.414  equals  the  square  root  of  2.  The  moment  of  inertia  is  the  sum 
of  the  products  of  the  weight  of  each  particle  into  the  square  of  its  distance  from 
the  pivot  round  which  the  mass  rotates:  it  is  therefore  not  only  desirable  when 
rapid  motion  is  to  be  produced  by  a  weak  force,  that  the  weight  should  be  small, 
but  also  that  it  should  be  near  the  pivots.  No  harm  is  done,  however,  by  putting 
the  pivots  far  from  the  points  of  contact,  because  we  thereby  diminish  the  angle 
through  which  the  armature  has  to  move  between  the  contacts;  so  that  if  we  halve 
the  angle  and  double  the  moment  of  inertia,  the  one  change  exactly  compensates 
the  other." 

It  is  evident,  too,  that  the  forward  and  backward  movement  of  the  iron 
armature  has  a  bearing  upon  the  efficiency  of  the  magnetic  circuit,  as  the  rela- 
tive position  of  the  armature  at  a  given  instant  with  respect  to  the  pole-faces 
influences  the  magnetic  condition  of  the  cores.  The  magnetic  circuit  is  most 
efficient  when  the  armature  is  in  contact  with  the  cores,1  the  efficiency  di- 
minishing rapidly  according  to  the  distance  to  which  the  armature  is  removed 
from  the  cores.  The  greater  the  mass  of  iron  in  the  cores,  the  greater  the 
weight  of  the  armature  and  the  slower  it  moves,  the  greater  will  be  the 
influence  tending  to  reduce  the  speed  of  signaling. 

The  length  of  gap  through  which  the  armature  tongue  is  required  to 
travel  should  be  made  as  short  as  practicable,  as  the  less  the  distance  through 
which  the  armature  moves,  the  more  rapidly  the  signals  may  be  made  to 
succeed  each  other  in  forming  letters  and  words. 

REDUCING  THE  TIME-CONSTANT  OF  RECEIVING  RELAYS 

With  a  given  instrument  there  are  several  ways  of  reducing  the  inductance 
without  altering  the  construction  of  the  magnets  and  without  increasing  the 
ohmic  resistance  of  the  windings.  The  iron  heel-piece  may  be  replaced  with 
a  brass  heel-piece,  thus  interrupting  the  continuous  magnetic  circuit.  The 
individual  windings  of  the  coils  of  the  magnets  may  be  connected  in  multiple 
instead  of  in  series  and  thereby  effect  a  reduction  of  the  total  self-induction 
of  the  instrument. 

By  altering  the  length  or  the  diameter;  or  both,  of  the  iron  cores,  the  mag- 
netic circuit  may  be  shortened  or  lengthened.  The  shorter  the  core  employed 
and  the  less  its  diameter,  the  less  will  be  the  self-induction  in  the  windings  sur- 
rounding the  cores.2  It  is  plain  that  the  period  D  may  be  reduced  in  duration, 

K. 

1  It  should  be  remembered  that  efficiency  of  the  magnetic  circuit  is  not  necessarily  an 
advantage  in  relay  signaling. 

2  Practically,  there  are  limits  to  which  the  reduction  in  dimension  of  core  may  be  car- 
ried.    See  Chapter  VI,  under  the  head  "  Electromagnetism  and  Electromagnets." 


SPEED  OF  SIGNALING  217 

by  increasing  the  resistance  R  or  by  decreasing  the  inductance  L  of  a  given 
relay,  and  as  there  are  plainly  evident  objections  to  increasing  the  resistance 
the  object  should  be  to  do  all  possible  toward  reducing  the  inductance  of  the 
relay.  How  well  this  has  been  accomplished  in  certain  types  of  receiving 
relay  is  evidenced  by  the  fact  that  speeds  as  high  as  400  words  per  minute  have 
been  attained  in  practice. 

Placing  the  windings  of  the  individual  coils  in  multiple  results  in  a  reduc- 
tion of  the  effective  ampere-turns  of  the  relay.  Suppose  for  instance  that  the 
two  coils  of  a  relay  are  connected  in  series,  each  coil  having  1,000  turns 
of  wire,  and  that  the  current  in  the  circuit  which  includes  the  windings  of  the 
relay  has  a  strength  of  50  milliamperes,  it  is  evident  that  each  coil  will  have 
50  ampere-turns.  If  now  the  coils  are  connected  in  multiple,  a  joint-circuit 
will  be  formed  through  the  two  coils,  with  the  result  that  the  5o-m.a.  current 
will  divide  equally  giving  25  m.a.  in  each  coil,1  or  the  total  ampere-turns  for 
both  coils  will  be  50  instead  of  100  as  is  the  case  where  the  two  coils  are  con- 
nected in  series.  It  is  evident  also  that  the  counter-e.m.f.  due  to  self-induc- 
tion is,  in  the  multiple  arrangement,  considerably  less  than  with  both  coils 
connected  in  series. 


Magnet  windings  connected  Magnet  windings  connected  in 

in  series.  multiple. 

FIG.    183. 

Figure  183  shows  on  the  left  an  end  view  of  a  pair  of  coils  having  their 
windings  connected  in  series  and  on  the  right  an  end  view  of  a  pair  of  coils 
with  their  windings  connected  in  multiple. 

SHUNTED  CONDENSER  METHOD 

The  effect  of  self-induction  in  a  relay  may  be  neutralized  or  " balanced" 
by  means  of  the  arrangement  depicted  in  Fig.  184,  where  R  represents  the 
winding  of  a  receiving  relay,  NIR  a  non-inductive  resistance  having  a  total 
range  about  equal  to  the  resistance  of  the  line,  or  the  rest  of  the  circuit,  and 
C  an  adjustable  condenser.  When  the  key  is  closed  the  condenser  is  given 
a  charge  as  a  result  of  the  potential  difference  across  the  resistance  coil 
NIR  (knowing  the  value  of  the  e.m.f.  applied  to  the  line,  and  the  resistance 

1  This  is  true  only  where  changing  the  series  circuit  into  a  joint  path  does  not  appreciably 
increase  the  current  value  in  the  circuit. 


218 


AMERICAN  TELEGRAPH  PRACTICE 


of  the  whole  circuit,  the  difference  of  potential  at  this  point  may  be  cal- 
culated by  the  fall  of  potential  method)  placed  in  shunt  with  the  condenser. 
It  is  required  that  the  capacity  of  the  adjustable  condenser  and  the  resistance 
NIR  be  so  adjusted  that  when  the  key  is  opened  the  discharge  from  the  con- 
denser will  be  equal  to  that  from  the  coils  of  the  relay  R.  If  the  resistance 
NIR  is  made  approximately  equal  to  that  of  the  rest  of  the  circuit,  the  proper 


NIR 


FIG,   184. — Shunted  condenser  method  of  balancing  the  self  induction  of  a  receiving  relay. 

condenser  adjustment  may  be  obtained  by  working  the  circuit  at  maximum 
speed,  and  then  altering  the  capacity  of  the  condenser  until  the  received 
signals  are  at  their  best. 

Where  high-speed  automatic  transmission  is  in  use  in  connection  with 
tape-marking  receivers  or  high-speed  electromagnetic  tape-punching  receivers, 
the  application  of  the  shunted  condenser  makes  possible  considerably  higher 
rates  of  working,  especially  where  the  line  so  operated  is  not  of  unusual  length. 


CHAPTER  XII 
SINGLE-LINE  REPEATERS 

The  length  of  telegraph  circuit  which  may  be  operated  satisfactorily 
depends  upon  the  prevailing  weather  conditions  which  affect  the  insulation 
resistance  of  the  line,  upon  the  number  of  intermediate  offices  connected  into 
the  circuit,  upon  the  method  of  transmission  employed,  and  upon  the  speed 
at  which  the  circuit  is  to  be  worked. 

From  what  was  stated  in  the  preceding  chapter  in  regard  to  the  properties 
of  telegraph  circuits  it  is  apparent  that  the  varying  conditions  experienced 
should  be  met  with  a  variety  of  circuit  arrangements  affording  flexibility  of 
plant  adequate  to  maintain  constant  service  no  matter  what  the  conditions 
or  the  service  requirements  may  be. 

The  difficulties  arising  from  lowered  line  insulation  may  necessitate  short- 
ening the  sections  of  line  operated  direct,  at  least  until  weather  conditions 
are  more  favorable;  or  if  the  low  insulation  obtaining  is  due  to  other  causes, 
until  normal  insulation  has  been  restored. 

The  number  of  offices  connected  into  an  individual  circuit;  in  most  cases 
depends  upon  traffic  and  service  requirements;  but,  if  from  the  electrical 
standpoint  the  number  of  offices  is  excessive  and  the  line  long,  it  is  found  that 
during  wet  weather  the  relays  connected  in  the  circuit  at  offices  near  the  mid- 
dle of  the  line  (or  where  battery  is  applied  to  the  line  at  one  end  only,  the 
relays  remote  from  the  battery)  operate  on  greatly  reduced  variations  in 
current  strength  when  keys  are  opened  and  closed  in  the  act  of  signaling. 

The  bearing  which  methods  of  transmission  and  signaling  speeds  have 
upon  the  length  of  circuit  which  may  be  operated  satisfactorily  relates  to 
receiving-end  current  values,  which  in  turn  are  dependent  upon  the  resistance, 
leakage,  capacity,  etc.,  of  the  line  wire.  As  these  factors  have  values  prac- 
tically directly  proportional  to  the  length  of  the. line,  it  is  obvious  that,  as 
previously  stated,  there  are  critical  lengths  of  line  which  may  be  operated 
direct  where  a  given  circuit  efficiency  is  to  be  maintained. 

It  would  be  possible  to  operate  a  continuous  circuit  across  the  American 
continent  (3,500  miles),  but  the  signals  would  have  to  be  transmitted  so 
slowly  that  the  circuit  would  be  highly  inefficient  from  a  telegraphic  stand- 
point, and  impossible  commercially. 

If  the  3,5oo-mile  line  were  divided  into  sections  of  approximately  500 
miles  each,  then  by  means  of  automatic  repeaters  located  at  the  junctions 
of  the  various  sections,  the  two  terminal  offices  located  3,500  miles  apart 

219 


220  AMERICAN  TELEGRAPH  PRACTICE 

i 

can  communicate  directly,  just  as  if  the  circuit  joining  the  two  offices  were 
continuous  and  had  battery  applied  at  the  terminals  only. 

In  this  case,  however,  the  speed  at  which  the  entire  circuit  may  be  oper- 
ated will  be  that  of  the  slowest  section  less  the  loss  in  repeaters.  It  is  obvious 
that  the  slowest  5oo-mile  section  will  have  a  circuit  efficiency  or  signaling 
speed  much  greater  than  that  of  the  entire  line  operated  as  one  3,5oo-mile 
section.1 

With  adequate  supervision  and  proper  maintenance  of  repeater  equip- 
ment, a  given  line  800  miles  long  and  having  a  speed  of  30  words  per  minute 
will  have  its  speed  possibilities  increased  fourfold  by  the  introduction  of  a 
repeater  midway  between  the  terminal  stations,  thus  making  two  4oo-mile 
sections  having  speeds  of  120  words  per  minute. 

Were  the  8oo-mile  line  divided  into  four  2oo-mile  sections,  theoretically 
the  speed  of  the  circuit  would  be  22  times  120,  or  480  words  per  minute. 

As  elsewhere  explained,  the  presence  of  aerial  or  underground  cable  in  a 
telegraph  circuit  gives  to  that  section  of  the  conductor  carried  in  the  cable 
a  higher  KR  than  that  possessed  by  the  sections  carried  on  pole  lines  and  sepa- 
rated from  other  wires  by  an  air  space  of  12  in.  or  thereabouts.  As  the 
speed  of  the  whole  circuit  is  that  of  the  slowest  section,  it  follows  that  the 
speed  of  the  cabled  sections  constitutes  the  speed  of  the  circuit. 

A  simple  illustration  of  the  principle  of  the  repeater  is  shown  in  Fig.  81, 
where  the  signals  received  by  the  main-line  relay  R  are  repeated  into  the 
(t local"  or  sounder  circuit,  due  to  the  action  of  the  relay  armature  lever 
closing  and  opening  the  sounder  circuit  in  response  to  the  opening  and  closing 
of  the  main-line  circuit  through  the  key  K. 

Figure  185  shows  three  stations  A,  B,  and  C.  Manipulating  the  key  K 
a,t  A  operates  the  relays  at  A  and  at  B,  and  it  may  be  noted  that  there  is  a 
complete  electrical  circuit  from  the  ground  at  A,  throuth  the  battery,  key 
and  relay  at  A ,  then  over  the  line  wire,  through  the  relay  at  B  and  thence  to 
ground  at  that  point.  The  operation  of  the  relay  at  B  in  response  to  the 
manipulations  of  the  key  at  A  causes  the  armature  tongue  of  the  relay  at  B 
to  close  and  open  the  second  circuit  or  section  of  the  line  and  the  armature 
of  the  relay  at  C  is  caused  to  move  in  unison  with  the  armatures  of  the 

1  Calculation  will  show  that  a  line  3,500  miles  in  length  made  up  of  wire  having  a  resist- 
ance of  4  1/2  ohms  per  mile  will  have  a  line  resistance  of  15,750  ohms.  If  the  average 
insulation  resistance  of  the  line  is  3.9  megohms  per  mile,  with  the  line  open  at  the  distant 
end  the  total  leak  path  to  earth  will  have  a  resistance  of  1,114  1/3  ohms.  The  joint-resist- 
ance of  the  conductor  to  the  distant  ground,  combined  with  the  various  leak  paths  to  ground 
distributed  along  the  line,  will  be  1,040  ohms.  Therefore,  with  battery  applied  at  one  end 
of  the  line  only,  an  e.m.f.,  of  1,417.5  volts  would  be  required,  with  a  sending  current  of 
1,362  milliamperes  to  maintain  a  received  current  of  90  milliamperes  at  the  distant  end  of 
the  circuit — 1,272  milliamperes  having  leaked  away  to  earth  due  to  imperfect  line  insulation. 

As  explained  elsewhere  in  this  work  it  is  inadvisable  to  employ  voltages  in  excess  of 
400  in  the  operation  of  telegraph  lines. 


SINGLE-LINE  REPEATERS 


221 


relays  at  A  and  B.  Thus  the  2oo-mile  line  is  divided  into  two  zoo-mile 
sections,  and  the  speed  possibilities  of  the  whole  circuit  correspondingly 
increased. 

With  the  simple  arrangement  shown  in  Fig.  185,  while  station  C  at  the 
end  of  the  second  section  will  receive  the  signals  transmitted  by  station  A 
at  the  beginning  of  the  first  section,  it  is  apparent  that  station  C  is  unable 
to  transmit  signals  to  either  station  B  or  station  A,  owing  to  the  fact  that 
manipulation  of  the  key  at  C  has  no  effect  upon  the  relay  at  B. 


B  C 


FIG.  185. 

In  order  to  maintain  operation  in  either  direction,  it  is  essential  that 
station  B  be  equipped  with  a  combination  of  instruments  which  may  be 
controlled  by  the  key  at  C.  So  that  C  may  send  to  A ,  B  should  have  a  set 
of  automatic  repeaters,  consisting  of  two  relays  and  two  transmitters.  This 
arrangement  is  called  a  full  set  of  repeaters.  The  conditions  desired  might 
be  represented  as  in  Fig.  186.  A  signal  from  the  east  must  operate  the 


FIG.  186. 

east  relay  and  west  transmitter,  but  must  not  operate  the  west  relay  or  the 
east  transmitter  and,  vice  versa,  a  signal  from  the  west  must  operate  the 
west  relay  and  the  east  transmitter  and  must  not  operate  the  east  relay  or 
west  transmitter. 

A  description  of  the  various  methods  employed  to  accomplish  this 
amounts  to  a  description  of  the  principles  involved  in  the  design  and  opera- 
tion of  the  different  repeaters  in  use,  and  in  what  follows,  descriptive  of  the 


222 


AMERICAN  TELEGRAPH  PRACTICE 


various  standard  types  of  repeater,  the  student  should  direct  his  attention 
to  the  means  availed  of  to  hold  one  side  of  a  repeater-set  silent  while  the 
other  side  is  operating. 

WEINY-PHILLIPS  REPEATER 

Figure  187  shows  the  local  and  main-line  wiring  of  a  full  set  of  Weiny- 
Phillips  repeaters,  in  which  R  and  R'  are  the  relays  and  T  and  T  the  trans- 
mitters. The  " jacks"  /  represent  the  switchboard  terminals  of  the  relay 
and  transmitter  circuit  extensions  from  the  repeaters. 

The  organized  apparatus  illustrated  in  Fig.  187  has  its  wiring  so  arranged 
that  the  local  circuits  are  operated  by  means  of  gravity  or  other  primary 
battery.  Fig.  188  shows  the  same  repeater  equipment  with  the  connections 
so  arranged  that  the  local  circuits  are  fed  from  a  dynamo  source  of  e.m.f. 


FIG.   187. — Weiny-Phillips  single-line  repeater.    Local  and  main-line  wiring.    Transmitters 
and  holding-coils  operated  from  gravity  battery. 

In  Figs.  187  and  188  the  shorter  magnet  mounted  above  the  main-line 
magnets  of  the  relays  is  wound  differentially.  The  diagrams  show  that  three 
wires  enter  the  smaller  magnet  and  the  manner  in  which  they  are  wound 
around  the  core  is  depicted  in  Figs.  189  and  190. 

In  Fig.  189,  one  terminal  of  the  battery  is  shown  grounded  while  the 
other  terminal  is  shown  connected  differentially  with  two  equal  windings 
of  the  magnet.  The  current  divides  at  A ,  half  going  through  each  coil.  It 
may  be  observed  that  the  direction  of  the  winding  of  one  coil  is  opposite  to 
that  of  the  other.  Thus,  when  current  flows  through  the  wire  B,  the  mag- 
netization of  the  core  due  to  the  action  of  current  in  the  coil  A-C  is  neu- 
tralized by  the  presence  of  current  in  the  coil  A-D,  and  as  a  result  the 
core  is  not  magnetized  at  all;  so  that  the  retractile  spring  attached  to  the 
armature  holds  the  latter  in  the  "open"  position  shown  in  Fig.  189. 


SINGLE-LINE  REPEATERS 


223 


224 


AMERICAN  TELEGRAPH  PRACTICE 


If,  however,  while  the  coil  A-C  remains  closed,  the  coil  A-D  is  opened,  as 
in  Fig.  190,  the  core  will  be  magnetized  due  to  the  presence  of  current  in  the 
coil  A-C  while  no  current  exists  in  coil  A-D,  the  latter  no  longer  neutralizing 
the  magnetic  effect  of  the  former.  The  armature,  therefore,  is  attracted  and 
held  in  the  "closed"  position  as  shown  in  Fig.  190. 


FIG.  189.  FIG.  190. 

FTGS.  189  AND  190. — Differential  winding  of  the  holding-coil,  Weiny-Phillips  repeater. 

It  is  by  means  of  this  extra  magnet  and  extra  local  batteries  that  the 
continuity  of  the  line  which  is  repeating  into  another  line  is  preserved  in 
the  Weiny-Phillips  repeater. 

The  "extra"  magnet  consists  of  but  one  coil  inclosed  in  a  soft  iron  shell 
open  at  the  front  or  armature  end  and  closed  at  the  opposite  end  except 
for  a  hole  at  the  center  through  which  the  end  of  the  iron  core  projects. 


FIG.  191. — Repeater  transmitter. 

It  may  be  seen  (Fig.  187)  that  the  extra  magnet  and  the  main-line  magnets 
actuate  the  same  armature,  the  extra  or  differential  magnet  being  energized 
by  a  local  battery  and  the  main-line  magnets  by  current  traversing  the 
main-line  circuit.  When  both  main-line  relays  are  closed  .the  local  con- 
nections are  such  that  the  local  current  divides  equally  between  the  two 
windings  of  the  extra  magnet,  so  that  the  armature  is  held  in  the  closed 
position  by  the  action  of  the  main-line  current.  Should  the  distant  station 
to  the  east  or  to  the  west  open  the  line,  the  consequent  opening  of  the  local 
contact-points  of  the  repeater  relay,  and  of  the  transmitter  which  it  controls, 


SINGLE-LINE  REPEATERS 


225 


results  in  opening  one  of  the  windings  of  the  differential  magnet.  This 
permits  the  current  in  the  companion  coil  to  magnetize  the  core  and  hold 
the  armature  of  the  relay  in  the  closed  position  until  the  main-line  circuit 
is  again  closed. 

Figures   191   and   192   show  photographic  reproductions  of  a  Weiny- 
Phillips  transmitter  and  relay  respectively. 


FIG.  192. — Weiny-Phillips  repeater  relay  showing  holding-coil  mounted  above  the  main- 
line magnets. 


,.  Compression  Spring 


OPERATION  OF  THE  WEINY-PHILLIPS  REPEATER 

Suppose  that  in  Fig.  187  a  line  wire  extending  west  of  the  repeater 
station  is  connected  to  the  repeater  set  through  the  pin-jack  /  and  that  a  line 
extending  east  is  connected  to  the  set  through  the  pin-jack  on  the  right.  If 
the  west  line  is  opened  (by 
opening  the  signaling  key  at 
the  distant  station,  or  other- 
wise) the  relay  R  is  deprived 
of  current,  and  as  current  is 
flowing  through  both  windings 
of  the  differential  magnet 
mounted  above  the  main-line 
magnets  of  R,  there  is  no  at- 
tractive force  exerted  upon  the 
armature.  The  result  is  that 
the  retractile  spring  attached 
to  the  relay  armature  pulls  the 


Insulation'' 
Compression' 


FIG.  193. — Enlarged  view  of  the  main  line  contacts 
of  a  repeater  transmitter. 


latter  away  from  the  "  closed "  contact  point,  thus  opening  the  battery 
circuit  through  the  coils  of  transmitter  T.  This  in  turn  allows  the  actuating 
spring  attached  to  the  armature  of  T  to  open  one  of  the  circuits  of  the  differ- 
ential magnet  mounted  above  the  main-line  coils  of  relay  Rf,  thus  holding 

15 


226 


AMERICAN  TELEGRAPH  PRACTICE 


the  armature  tongue  of  that  relay  in  the  closed  position,  when  a  moment 
later  the  circuit  extending  to  the  east  is  opened  at  N.     If  the  circuits  are 


FIG.  194. — Local  and  main-line  connections  of  a  repeater  transmitter. 

now  traced  it  will  be  seen  that  the  local  circuit  through  the  magnets  of 
transmitter  T'  is  prevented  from  opening,  therefore  the  continuity  of  the 

circuit  extending  west  is  preserved, 
and  as  both  windings  of  the  differential 
magnet  of  relay  R  are  energized,  the 
armature  of  the  latter  is  withdrawn 
from  the  closed  contact  point  as  long 
as  the  western  circuit  is  held  open. 
As  soon,  however,  as  the  distant 
western  station  closes  his  signaling 
key,  relay  R  will  be  energized,  thus 
attracting  its  armature,  which  in  turn 
closes  the  battery  circuit  through  trans- 
mitter T,  and  the  signal  is  repeated 
into  the  east  line  as  a  consequence  of 
FIG.  195.— New  form  of  repeater  trans-  the  altered  position  of  the  armature 
mitter  having  a  vertical  lever  in  place  of  of  transmitter  T. 

the    horizontal    lever  shown  in  Figs.  191         Figure  193  shows  an  enlarged  view 
and  I94<  of     the     main-line    contacts    of    the 

transmitter. 

Figure   194  shows  the  connections  of  a  standard  pattern  of  Weiny- 


SINGLE-LINE  REPEATERS 


227 


Phillips  transmitter  with  the  fulcrums  of  the  levers  and  the  lever  actuating 
springs  in  their  proper  relations. 

Figure  195  is  a  diagrammatic  view  of  a  recently  introduced  form  of 
Weiny-Phillips  transmitter,  having  vertical  or  upright  levers  in  place  of 
the  horizontal  levers  shown  in  the  other  figures. 

THE  ATKINSON  REPEATER 

In  the  Atkinson  repeater  the  method  availed  of  to  hold  the  transmitter 
main-line  contacts  closed  is  to  employ  the  lever  of  a  repeating  sounder  to 
form  a  shunt  path  around  the  contact  points  of  the  relay,  when  the  main-line 
circuit  through  the  relay  coils  is  opened.  This  prevents  the  local  circuit, 
including  the  magnet  windings  of  the  transmitter,  from  opening. 


East 


To  T1 


West 

FIG.  196. — Continuity-preserving  circuits  of  the  Atkinson  repeater. 


Figure  196  shows  a  portion  of  the  Atkinson  repeater  wiring  sufficient 
to  illustrate  the  theory  of  the  "holding"  arrangement.  It  will  be  seen 
that  the  repeating  sounder  RS  is,  in  operation,  controlled  by  the  operation 
of  the  circuit  extending  to  transmitter  T'  in  the  other  half  of  the  set  (trans- 
mitter T'  not  shown).  At  the  critical  moment  the  contact  points,  between 
which  the  armature  of  relay  R  plays,  are  short  circuited,  due  to  the  opening 


228 


AMERICAN  TELEGRAPH  PRACTICE 


of  RS,  and  the  local  battery  LB  continues  to  energize  the  magnets  of  trans- 
mitter T,  thus  preserving  the  continuity  of  the  line  east. 

Figure  197  shows  the  complete  theoretical  wiring  of  a  full  set  of  Atkinson 
repeaters. 

West  Line 


[FiG.  197. — The  Atkinson  single-line  repeater.    Local  and  main-line  wiring. 


OPERATION  OF  THE  ATKINSON  REPEATER 

As  the  distant  western  office  opens  the  signaling  key,  thereby  opening 
the  main-line  circuit,  relay  Rf  "opens"  and  releases  its  armature  lever 
which  is  drawn  back  by  the  retractile  spring  attached  to  it  (as  long  as  the 
distant  eastern  office  keeps  his  signaling  key  closed  relay  R  and  transmitter 
T  will  remain  closed,  provided,  of  course,  that  the  line  west  remains  closed 
at  the  same  time)  and,  when  the  distant  western  office  closes  his  key,  relay 
R'  is  energized  and  its  armature  immediately  closes  the  local  circuit  of  trans- 
mitter T',  the  result  of  which  is  that  the  main-line  eastern  battery  at  the 
repeater  station  is  placed  in  contact  with  the  line  east  through  the  main-line 
contact  points  of  transmitter  Tf.  It  will  be  observed,  however,  that  the 
altered  position  of  the  lever  of  transmitter  T'  results  in  the  withdrawal  of 
the  armature  of  RS,  from  the  upper  contract  point,  thus  removing  the 


SINGLE-LINE  REPEATERS 


229 


short  circuit  across  the  points  of  relay  R.  Transmitter  T,  however,  has 
not  had  time  to  open,  as  at  the  instant  that  RS,  opened  the  shunt  circuit, 
relay  R  closed,  due  to  the  presence  of  current  in  its  coils.  The  passage  of 
signals  in  the  opposite  direction  through  the  repeater  might  be  traced  in  the 
same  manner.  In  each  case  it  will  be  found  that  the  opening  of  the  repeating 
sounder  due  to  the  opening  of.  one  transmitter  results  in  the  opposite  trans- 
mitter being  held  closed  until  the  main-line  circuit  through  the  relay  is  again 
closed. 

Figure  198  shows  the  actual  binding-post  connections  of  a  full  set  of  Atkin- 
son repeaters. 


Line  East 


Line  West 


'  Main 
.Bat 


Main 
bat, 


—i —  — i— 

i  •  i  . 

FIG.  198. — Atkinson  repeater,  binding-post  connections. 


THE  GHEGAN  REPEATER 

Figure  199  shows  the  wiring  of  a  full  set  of  Ghegan  repeaters  arranged 
for  gravity-battery  locals.  Fig.  200  shows  the  connections  where  dynamo 
currents  are  employed  to  operate  the  transmitters. 


OPERATION  OF  THE  GHEGAN  REPEATER 

Referring  to  Fig.  199:  When  the  signaling  key  at  the  distant  western  office 
or  the  key  in  the  western  relay  circuit  at  the  repeater  station  is  opened  the 
various  armatures  assume  the  positions  shown.  The  armature  of  relay  Rr 
first  falls  back  and  opens  the  local  circuit  of  transmitter  Tf,  which  in  turn 


230 


AMERICAN  TELEGRAPH  PRACTICE 


West 


East 


FIG.  199. —  Ghegan  single-line  repeater.     Theoretical  connections,  using  gravity  battery 

to  operate  the  transmitters. 


FIG.  200. — Ghegan  repeater  arranged  for  dynamo  local  currents. 


SINGLE-LINE  REPEATERS  231 

opens  the  eastern  circuit  at  S'rf,  thereby  releasing  the  armature  of  relay  R. 
As  the  armature  of  the  relay  is  drawn  into  contact  with  the  back-stop,  how- 
ever, the  local  circuit  of  transmitter  T  is  not  affected,  as,  before  the  eastern 
circuit  was  opened  at  S'r',  the  shunt  circuit  around  the  local  contacts  of 
relay  R  was  closed  at  M'O'.  Now,  when  the  distant  western  station  closes 
his  key,  the  armature  of  relay  Rf  automatically  closes  the  circuit  of  trans- 
mitter T'j  which  in  turn  first  closes  the  circuit  extending  east  at  Sr  rf,  and 
after  a  sufficient  time  has  elapsed  to  allow  the  armature  of  relay  R  to  reach 
its  closed-contact  point,  opens  the  shunt  circuit  of  transmitter  T  at  M'O'. 
If  while  the  distant  western  office  is  sending,  the  distant  eastern  office 
should  interrupt  or  " break,"  the  armature  of  relay  R,  will  remain  on  its 


FIG.  201. — Ghegan  repeater  transmitter. 

back  contact,  thus  breaking  the  local  circuit  of  transmitter  T,  on  the  first 
downward  stroke  of  the  superposed  armature  of  transmitter  T',  and  open  the 
western  circuit  at  S,  r. 

Figure  201  shows  a  photographic  view  of  the  transmitter  used  in  the 
Ghegan  repeater.  The  superposed  armature  mounted  above  the  regular 
armature  is  clearly  shown.  The  novelty  of  this  repeater  is  due  to  the  prin- 
ciple that  an  armature  on  being  drawn  toward  magnet  poles  itself  becomes  mag- 
netic by  induction,  and  the  closer  the  armature  approaches  the  poles  of  the 
magnet  the  stronger  the  induced  magnetism  becomes.  The  employment  of 
this  principle  insures  simultaneous  movement  of  the  two  armatures,  and  when 
the  latter  are  properly  adjusted  the  action  of  the  repeater  is  quite  rapid  and 
certain. 


232 


AMERICAN  TELEGRAPH  PRACTICE 

0 

THE  NEILSON  REPEATER 


The  unusual  feature  of  the  Neilson  repeater  is  that  but  one  local  battery 
is  required  for  the  relay  and  the  transmitter  of  each  half  of  the  set.  The 
relays  may  be  ordinary  main-line  single-contact  relays,  and  the  transmitter 
employed  may  be  either  the  regulation  repeater  transmitter  or  a  repeating 
sounder. 

Figure  202  shows  the  theoretical  connections  of  a  Neilson  full-set  single- 
line  repeater. 


FIG.  202. — Neilson  single- line  repeater.     Theory. 

R  and  R'  are  ordinary  i5o-ohm  main-line  relays.  T  and  Tf  may  be  regula- 
tion transmitters  of  from  4  to  10  ohms  resistance.  RS  and  RSf  are  repeating 
sounders  of  40  ohms  resistance. 

By  referring  to  Fig.  202  it  may  be  seen  that  if  the  main-line  relays  R  and 
R'  were  closed,  the  armatures  of  transmitters  T  and  T'  also,  would  be  in  the 
closed  position,  and  the  battery  circuits  of  RS  and  RS'  would  be  shunted  by 
the  armatures  of  relays  R  and  R'.  It  is  evident,  of  course,  that  with  the  relay 
armature  withdrawn  from  its  front  contact,  current  from  the  local  battery 
flows  through  the  magnet  coils,  both  of  the  transmitter  and  the  repeating 
sounder;  but  owing  to  the  great  difference  in  the  number  of  ampere-turns 
of  the  windings  of  the  4o-ohm  repeating  sounder  and  the  4-ohm  transmitter,  it 
is  easy  to  adjust  the  actuating  springs  attached  to  the  armature  levers  of  the 


SINGLE-LINE  REPEATERS  233 

two  instruments  so  that  when  this  condition  prevails  the  lever  of  the  trans- 
mitter will  remain  against  its  back-stop,  while  the  lever  of  the  repeating 
sounder  will  be  attracted  toward  its  closed  contact.  This  is  due  to  the  exist- 
ing current  volume  in  the  circuit  being  too  low  to  actuate  the  transmitter, 
but  of_sufficient  strength  to  operate  the  repeating  sounder. 

By  tracing  the  connections  it  will  be  seen  that  with  the  armature  of  RS 
in  the  position  shown  in  Fig.  202,  current  flows  through  the  magnet  windings 
of  RS'  and  holds  its  armature  closed,  and  further,  that  as  long  as  RS'  remains 
closed,  RS  must  remain  open,  due  to  the  fact  that  its  windings  are  now  short- 
circuited.  The  result  is  that  when  RS'  is  closed,  transmitter  T  is  closed,  and 
when  RS  is  closed,  transmitter  T'  is  closed. 

OPERATION  OF  THE  NEILSON  REPEATER 

With  the  main-line  circuits  east  and  west  of  the  repeating  station  closed, 
both  relays  and  both  transmitters  will  be  closed,  while  both  of  the  repeating 
sounders  will  be  open. 

When  the  distant  eastern  office  opens  his  main-line  key,  relay  R  releases 
its  armature,  thus  opening  the  short  circuit  around  the  coils  of  RS.  This 
places  the  repeating  sounder  in  series  with  transmitter  T,  the  latter  releasing 
its  armature.  The  opening  of  T  automatically  opens  the  circuit  extending 
west,  and  releases  the  armature  of  relay  R' ',  thereby  removing  the  short 
circuit  which  the  armature  had  maintained  across  the  coils  of  RSf.  At  the 
instant,  however,  that  T  opened,  repeating  sounder  RS  closed,  preventing 
the  closing  of  RS'  or  the  opening  of  transmitter  T',  thus  the  continuity  of  the 
line  east  is  preserved. 

When  the  signaling  key  at  the  distant  eastern  office  is  closed,  relay  R  is 
energized,  closing  the  local  circuit,  thereby  permitting  transmitter  T  to  close 
the  line  extending  west  from  the  repeater  station.  RS  now  being  short-cir- 
cuited by  the  armature  lever  of  relay  R,  loses  its  magnetism,  and  as  a  result 
the  short  circuit  around  the  coils  of  RS'  is  removed.  At  the  same  instant, 
however  (as  R'  is  now  energized),  the  other  short  circuit  around  RS'  is 
closed.  Thus  it  may  be  seen  that  T'  is  held  closed  and  RS'  remains  open 
regardless  of  whether  the  line  east  is  open  or  closed,  so  that  while  the  distant 
eastern  station  is  transmitting,  transmitter  T'  at  the  repeater  station  remains 
closed. 

The  operation  of  " breaking"  or  of  repeating  signals  from  the  western 
circuit  to  the  eastern  circuit  may  readily  be  traced  from  the  above  description. 

With  the  instrument  resistance  values  as  herein  given  it  is  customary  to 
use  four  cells  of  gravity  battery  in  each  half  of  the  repeater.  Where  dynamo 
currents  are  availed  of,  suitable  reducing  resistances  are  employed  to  regulate 
the  current  values  in  the  local  circuit. 

Figure  203  shows  the  actual  binding-post  connections  of  a  full  set  of 
Neilson  repeaters. 


234 


AMERICAN  TELEGRAPH  PRACTICE 


The  wiring  extensions  shown  leading  to  the  main  switchboard  usually  are 
brought  to  pin-jacks,  so  that  one  wire  from  each  half  of  the  repeater  may  be 
connected  through  a  main-line  battery  to  ground,  while  the  other  wire  from 
the  same  side  is  connected  by  means  of  a  cord  and  wedge,  through  a  spring- 
jack  to  the  desired' main-line  wire  extending  in  any  direction.1 


To  Switchboard 


To  Switchboard 


FIG.  203. — Binding-post  connections  of  a  Neilson  single-line  repeater. 


THE  TOYE  REPEATER 

In  the  Toye  repeater,  no  extra  magnets  or  repeating  sounders  are  re- 
quired. The  main-line  relay  of  the  wire  being  repeated  into  is  prevented 
from  releasing  its  armature,  by  shifting  the  main  battery  from  the  line  to  an 
artificial  circuit  consisting  of  a  resistance  box  or  rheostat,  having  a  resistance 
approximately  equal  to  that  of  the  regular  line  wire  to  the  distant  station. 
The  operation  of  shifting  the  battery  from  main  to  artificial  line  is  performed 
by  the  transmitter. 

Operation  of  the  Toye  Repeater. — By  referring  to  Fig.  204  it  may  be 
seen  that  should  the  distant  eastern  office  close  his  main-line  key  the  armature 
of  relay  R  at  the  repeating  station  will  be  attracted,  thereby  closing  the  local 
battery  circuit  of  transmitter  T,  placing  the  lower  lip  of  the  transmitter  lever 
points  in  contact  with  the  line  extending  to  the  distant  western  station. 
This  places  the  western  battery  to  line  west.  While  the  distant  eastern 
station  continues  to  transmit,  relay  R'  and  transmitter  Tf  remain  closed. 
The  manner  in  which  the  silence  of  these  two  instruments  is  maintained  con- 
1  It  will  be  shown  in  Chapter  XVIII  dealing  with  multiplex  repeaters  that  full  sets  of 
repeaters  are  usually  so  provided  with  table  switches,  that  they  may  be  "split"  or  divided 
so  that  one-half  of  the  set  may  be  used  to  connect  a  single  line  into  a  duplex  set,  or  into  one 
side  of  a  quadruplex  set,  at  a  repeater  station. 


SINGLE-LINE  REPEATERS 


235 


West  Line 


Rheostat  Eastern  :=; 

R  H  Battery^r 


Ground 


I 


East  Line 


iE  Western 
-^-Battery 


I 


Ground 


FIG.  204. — Theory  of  the  Toye  single-line  repeater. 


Line  East 


Line  West- 


— D  O  Q  Q  Q 

f;-_\V^ 


i 


Trans. 


Rheostat 


T 


ft 


FIG.  205. — Binding-post  connections  of  the  Toye  repeater. 


236  AMERICAN  TELEGRAPH  PRACTICE 

stitutes  the  unusual  feature  of  the  Toye  repeater.  It  is  evident  that  as  long 
as  relay  Rf  remains  closed,  transmitter  T'  will  remain  closed,  thus  preserving 
the  continuity  of  the  line  east  while  signals  are  being  transmitted  from  the 
east  to  the  west  through  the  repeaters. 

As  transmitter  T  applies  and  removes  the  western  battery  to  and  from  the 
west  line  in  response  to  the  operation  of  relay  R,  relay  R'  is  prevented  from 
opening  due  to  the  fact  that  the  western  battery  when  not  in  contact  with  the 
line  west  is  given  a  path  to  earth  through  the  rheostat  RH  by  way  of  the  tongue 
and  lip  of  transmitter  T,  thus  holding  relay  R'  closed  until  the  western  station 
desires  to  "break"  or  to  begin  transmitting  to  the  eastern  station.  The 
transmission  of  signals  from  the  west  to  the  east  is  accomplished  by  the  re- 
verse process  of  that  above  described. 

Figure  205  shows  the  actual  binding-post  connections  of  a  full  set  of  Toye 
repeaters. 

In  the  operation  of  the  Toye  repeater  it  will  be  seen  that  the  main-line 
batteries  are  constantly  in  use,  being  at  all  times  applied  either  to  the 
main  lines  or  to  the  artificial  lines.  This  means  excessive  consumption  of 
current,  and  constitutes  an  undesirable  feature  of  this  type  of  repeater.  It  is 
evident  also,  that  as  a  particular  set  of  repeaters  is  applied  to  lines  of  different 
lengths  (having  different  resistance  values)  the  adjustment  of  the  artificial- 
line  resistance  must  be  varied  to  equal  that  of  the  line  or  lines  connected 
through  the  repeaters,  in  order  to  have  equal  magnetic  pull  on  the  armatures 
of  the  relays  whether  the  relay  is  in  circuit  with  the  artificial  line  or  the  main 
line.  Naturally  it  is  essential  to  have  regular  action  of  the  relay  if  satis- 
factory repeating  is  to  be  accomplished. 

THE  MILLIKEN  REPEATER 

The  development  of  practical  telegraph  repeaters  began  in  the  United 
States  about  the  year  1855.  During  the  ensuing  10  years  satisfactory  re- 
peaters were  brought  out  by  several  well-known  workers,  among  whom 
might  be  mentioned  J.  J.  Speed,  Jr.,  Farmer  and  Woodman,  James  J. 
Clark,  George  B.  Hicks,  and  George  F.  Milliken.  The  name  of  the  latter  has 
not  been  mentioned  last  as  an  indication  that  he  followed  the  others  in  the 
development  of  telegraph  repeaters;  for  in  reality  he  was  one  of  the  very 
first  to  achieve  success  in  this  line,  but  because  his  product  has  survived 
longer  than  that  of  any  of  the  others. 

In  the  Milliken  repeater  the  transmitter  armature  lever  is  held  in  the 
closed  position  mechanically  through  the  agency  of  an  extra  magnet,  the 
armature  of  which  (when  withdrawn  by  its  retractile  spring)  is  in  mechanical 
contact  with,  and  holds  the  armature  of  the  relay  in  the  closed  position 
during  the  periods  when  there  is  no  magnetism  in  the  cores  of  the  relay. 
The  armature  lever  of  the  extra  magnet  is  equipped  with  a  retractile  spring 


SINGLE-LINE  REPEATERS 


237 


which  may  be  given  a  greater  tension  than  that  of  the  spring  attached  to 
the  lever  of  the  relay  proper  (see  Fig.  206),  which  provides  that  the  latter 
cannot  fall  back  and  open  the  transmitter  circuit  except  at  the  instant  that 
the  stronger  extra  magnet  is  attracting  its  armature  toward  its  closed  con- 
tact. Obviously  while  the  lever  of  the  extra  magnet  is  in  the  closed  position, 
the  lever  of  the  relay  is  free  to  move  backward  and  forward  in  response  to 
line  signals,  but  while  the  lever  of  the  extra  magnet  is  withdrawn  into  con- 
tact with  its  back-stop,  the  relay  lever  cannot  move,  regardless  of  what 
takes  place  in  the  circuit  of  which  the  windings  of  the  relay  form  a  part. 


West  Line _ 


East  Line 


FIG.  206. — Theory  of  the  Milliken  single-line  repeater. 

Operation  of  the  Milliken  Repeater. — Referring  to  Fig.  206:  when  the 
distant  western  office  opens  his  main-line  key,  relay  R  loses  its  magnetism, 
and,  owing  to  the  fact  that  the  extra  magnet  is  energized,  the  armature  of 
relay  R  will  fall  back  and  open  the  local  circuit  of  transmitter  T,  thus  re- 
moving the  main  line  battery  from  the  line  east.  When  the  armature  of 
transmitter  T  is  released,  it  automatically  opens  the  extra  local  circuit 
through  the  winding  of  EM1  which  results  in  the  armature  of  R1  being  held 
closed  preventing  transmitter  T1  from  opening  the  line  west.  Thus  the  con- 
tinuity of  the  circuit  is  preserved.  When  the  distant  western  office  closes 
his  key,  relay  R  is  energized,  resulting  in  the  closing  of  the  local  circuit  of 
transmitter  T,  placing  the  main  battery  to  line  east  through  relay  R1,  and 


238 


AMERICAN  TELEGRAPH  PRACTICE 


so  holding  transmitter  T1  closed  at  the  instant  that  the  armature  of  EM1 
is  attracted  due  to  the  closing  of  T. 

By  noting  what  takes  place  in  each  circuit  during  the  transmission  of 
signals  in  either  direction  through  the  repeater  and  during  the  operation  of 
breaking,  the  action  of  the  repeater  under  any  possible  condition  may 
easily  be  traced. 

Figure  207  shows  the  actual  binding  post  connections  of  a  full  set  of 
Milliken  repeaters. 


FIG.  207. — Binding-post  connections  of  the  Milliken  repeater. 


THE  HORTON  REPEATER 

As  in  the  case  of  all  other  repeaters,  the  distinguishing  feature  of  the 
Horton  repeater  is  the  method  employed  to  preserve  the  continuity  of  the 
sending  main-line  circuit  while  repeating  into  a  separate  main-line  circuit 
extending  in  another  direction. 

Figure  208  shows  the  wiring  of  a  full  set  of  Horton  repeaters.  It  may 
be  observed  that  the  wiring  of  the  transmitters,  relays,  and  extra  magnets 
is  similar  to  that  of  the  Milliken  repeater,  but  the  way  in  which  the  relay 
tongue  is  held  closed  at  the  critical  moment  is  different  from  the  retractile 
spring  arrangement  which  is  a  feature  of  the  Milliken.  By  referring  to 
Fig.  208  it  will  be  seen  that  the  wood  base  of  the  Horton  relay  is  higher  at 
one  end  than  at  the  other.  Due  to  the  force  of  gravity  the  armature  of  the 


SINGLE-LINE  REPEATERS 


239 


relay  has  a  natural  tendency  to  fall  forward  and  into  contact  with  the  front- 
stop  when  the  cores  of  the  extra  magnet  lose  their  magnetism  due  to  the 
opening  of  the  extra-local  transmitter  circuit.  It  is  at  once  apparent  that 
the  relay  armature  will  remain  in  contact  with  its  front-stop  regardless  of 
whether  or  not  there  is  current  in  the  main-line  winding  of  the  relay  magnets, 
but  only  so  long  as  the  retracting  magnet  is  not  energized.  When  the  re- 
tracting magnet  is  energized  the  armature  of  the  relay  will  be  withdrawn 
when  no  current  traverses  the  main  line  coils  of  the  relay.  When,  how- 
ever, both  the  retracting  and  the  main-line  coils  are  energized,  the  pull  of 
the  main-line  coils  aided  as  it  is  by  the  force  of  gravity  is  sufficient  to  over- 
come the  weaker  retracting  force  and  to  hold  the  armature  in  contact  with 


FIG.  208. — The  Horton  single-line  repeater. 

the  front-stop.  The  retractile  force  exerted  by  the  extra  magnet  may  be 
regulated  to  suit  the  requirements  in  a  given  case,  by  means  of  a  threaded 
adjusting  screw  which  is  attached  to  the  heel-piece  or  yoke  of  the  magnet. 
Operation  of  the  Horton  Repeater. — Figure  208  shows  all  circuits  closed. 
When  the  distant  western  office  opens  the  main-line  key,  the  current  through 
relay  R  is  interrupted,  releasing  its  armature  lever  which  is  drawn  into  con- 
tact with  the  back-stop  due  to  the  magnetism  of  the  extra  magnet.  The 
local  circuit  of  transmitter  T  is  thereby  opened,  resulting  in  the  tongue  of 
that  transmitter  moving  away  from  contact  with  the  line  east,  thereby  open- 
ing the  eastern  circuit  in  response  to  the  open  key  at  the  distant  western 
office.  At  the  instant  that  transmitter  T  opens,  the  current  traversing  the 
main-line  coils  of  relay  R1  is  interrupted,  and  at  first  sight  it  might  seem  that 
the  armature  of  relay  R1  would  instantly  be  drawn  back  by  the  extra  magnet 
thereby  opening  transmitter  T1  (the  very  thing  that  must  not  happen),  but  a 
glance  will  show  that  at  the  instant  transmitter  T  opens  the  circuit  through 
the  main-line  coils  of  relay  R1,  it  also  opens  the  extra  local  circuit  through 


240 


AMERICAN  TELEGRAPH  PRACTICE 


the  retracting  coils  of  relay  R1,  thereby  leaving  the  tongue  of  that  relay  in  the 
closed  position  and  unaffected. 

A  little  thoughtful  consideration  of  the  repeater  circuits  in  their  various 
relations,  with  the  aid  of  the  foregoing  description,  will  enable  the  student 
to  trace  the  operation  of  the  instruments  while  signals  are  being  passed 
through  in  either  direction.  It  is  instructive  also  to  observe  the  action  that 
takes  place  when  the  distant  eastern  office  is  sending  and  the  office  on  the 
line  west  desires  to  break.  The  same  action,  of  course,  would  take  place  on 
the  opposite  side  of  the  set  were  the  eastern  office  to  break  while  the  western 
office  is  sending. 

One  distinctive  advantage  that  the  Horton  repeater  has  over  other  types, 
is  in  the  matter  of  battery  economy.  One  gravity  cell  in  good  condition  is 
sufficient  to  operate  each  of  the  extra  local  circuits,  while  two  cells  in  good 
condition  are  sufficient  to  operate  each  transmitter  circuit. 

THREE -WIRE  REPEATER 

There  are  various  combinations  possible  for  working  three  wires  into  each 
other,  and  a  description  of  one  such  arrangement  adaptable  to  any  of  the 
forms  of  repeater  herein  described  is  given  herewith. 


South 


FIG.  209. — Three-way  single-line  repeater. 

Referring  to  Fig.  209:  when  all  circuits  are  closed,  current  from  the 
dynamo  flows  through  the  contact  points  of  the  eastern  relay  ER  to  C  where 
it  splits,  part  traversing  the  coils  of  ST'  thence  passing  to  ground  through  a 


SINGLE-LINE  REPEATERS 


241 


regulating  resistance.  Current  from  the  same  source  traverses  the  windings 
of  ET,  and  passes  thence  to  the  switch,  and  from  there  to  ground  via  the 
contact  points  of  SR.  The  closed-contact  points  of  transmitters  ET  and  ST' 
hold  the  lines  extending  south  and  west  closed,  while  the  local  circuits  are 
held  closed  through  relay  WR  and  transmitters  WT  and  ST. 

When  an  office  on  the  east  line  opens  his  key,  the  levers  of  the  instruments 
take  positions  as  indicated  in  Fig.  209.  While  the  east  is  sending  it  is  neces- 
sary that  transmitters  57"  and  WT  remain  closed  in  order  that  the  continuity 
of  the  transmitting  circuit  shall  be  preserved.  When  the  circuit  through 
ER  opens,  it  follows  that  ET  and  STf  open  at  the  same  time.  The  back-stop 
contacts  of  ET  open  the  extra  magnet  of  WR,  the  retractile  spring  of  which 
holds  the  contact  points  of  WR  closed,  preserving  intact  the  local  circuits, 


FIG.  210. — Three-way  single-line  repeater  arranged  for  gravity  battery  operation  of  trans- 
mitters. 

and  as  a  consequence,  also,  the  main  line  circuits  west  and  south,  through 
transmitters  WT  and  ST.  The  back  contacts  of  ST',  similarly,  open  the 
holding  magnet  circuit,  thus  holding  the  armature  of  SR  in  the  closed  posi- 
tion, preserving  intact  the  local  circuit  through  transmitter  WT. 

If  while  the  east  is  sending  into  the  western  and  southern  lines,  the  office 
on  the  south  line  should  desire  to  break,  the  opening  of  his  key  interrupts 
the  current  in  relay  SR,  which  automatically  removes  the  ground  connection 
of  the  local  circuits  through  ET  and  WT.  The  opening  of  the  transmitters 
is  due  to  the  fact  that  the  currents  from  the  two  dynamos  are  of  the  same 
polarity,  permitting  no  current  flow  in  the  circuit.  Whenever,  therefore, 
relay  SR  is  being  operated,  transmitters  ET  and  WT  repeat  the  signals 
into  the  west  and  east  lines. 

16 


242  AMERICAN  TELEGRAPH  PRACTICE 

The  arrangement  of  this  three-wire  repeater  where  gravity  battery  only 
is  available  is  illustrated  in  Fig.  210.  The  diagram  shows  the  local  circuits 
only.  The  arrows  indicate  the  direction  of  the  currents,  and  are  of  material 
aid  to  the  student  in  tracing  out  the  various  operations  that  take  place, 
with  transmission  in  any  given  direction. 

SELF-ADJUSTING  REPEATERS 

It  is  well  known  that  a  repeater  of  any  type  requires  intelligent  super- 
vision and  careful  adjustment  if  it  is  to  satisfactorily  do  the  work  expected 
of  it. 

From  what  has  heretofore  been  explained  in  regard  to  repeater  operation 
it  is  apparent  that  the  signals  transmitted  over  the  line  beyond  the  repeater 
'station  are,  in  a  sense,  second  hand.  While  the  manipulation  of  the  key  at 
the  sending  station  directly  controls  the  operation  of  the  relay  at  the  repeater 
station,  the  outgoing  signals  from  the  latter  office  are  produced  by  the 
transmitter  tongue  contacts.  This  makes  it  imperative  that  the  "breaks" 
shall  be  clear,  and  that  the  contacts  with  the  line  connection  be  regular  and 
positive;  otherwise  the  repeated  signals  will  not  be  exact  reproductions 
of  the  signals  received  by  the  relay.  Sudden  changes  in  weather  conditions 
along  the  line  must  be  watched,  and  the  repeater  adjustments  altered  to 
meet  the  altered  line  conditions  which  result  therefrom.  Also,  in  practice, 
it  is  found  that  the  individual  characteristics  in  the  sending  of  different 
operators  impose  upon  repeaters  the  requirement  that  they  shall  operate 
satisfactorily  on  different  adjustments. 

All  operators  are  not  capable  of  sending  firm  and  regular  signals  by  hand. 
The  signals  transmitted  by  a  particular  operator  may  reach  the  repeater 
station  too  " light"  to  permit  of  satisfactory  operation  of  the  local  circuits 
with  the  ordinary  adjustments  of  releasing  springs,  magnets,  and  armature 
travel.  In  such  cases  it  is  sometimes  possible  to  make  the  outgoing  signals 
" heavier"  by  reducing  somewhat  the  tension  of  retractile  springs,  by  moving 
magnet  cores  closer  to  armatures,  or  by  reducing  the  "play"  of  armature 
tongues  between  contact  points. 

In  order  to  insure  satisfactory  operation  of  repeaters,  it  is  customary  to 
have  repeater  attendants  in  charge  of  a  certain  number  of  sets,  whose  duties 
are  to  supervise  the  working  of  circuits  operated  through  repeaters.  In 
many  instances  it  is  found  advisable  to  provide  an  attendant  at  each  repeater 
station  to  watch  the  operation  of  an  individual  circuit.  Thus,  a  circuit 
extending  from  New  York  to  San  Francisco  may  pass  through  six  repeaters 
en  route,  and  if  the  circuit  is  an  important  one,  or  if  uninterrupted  service 
and  maximum  speed  is  desired,  at  each  of  the  six  repeater  stations  an  attend- 
ant (sometimes  referred  to  as  a  "rider")  is  assigned  to  watch  the  repeater 
operating  in  this  particular  circuit,  and  to  confine  his  undivided  attention  to 
the  working  of  this  circuit  only. 


SINGLE-LINE  REPEATERS 


243 


In  view  of  the  foregoing  it  is  no  wonder  that  many  attempts  have  been 
made  to  devise  a  repeater  that  will  be  self-adjusting,  or  a  repeater  that  will 
remain  permanently  adjusted  regardless  of  the  varying  conditions  obtaining 
in  the  circuit  on  either  side  of  the  repeater  station,  whether  the  changes  are 
due  to  sudden  weather  changes  or  to  altered  characteristics  of  transmission 
following  a  change  of  sending  operators. 


THE  D'HUMY  SELF-ADJUSTING  REPEATER 

This  repeater  is  designed  to  fill  a  special  field  where  certainty  of  operation 
is  required  at  all  times,  on  especially  poor  lines  where  operating  current 


FIG.  211. — d'Humy  self-adjusting  single-line  repeater. 

values  vary  to   a  degree  that  makes  ordinary  single  repeater  operation 
exceedingly  difficult. 

Any  change  in  current  value  from  four  or  five  milliamperes  and  upward 
will  suffice  to  operate  this  type  of  repeater.     The  repeater  relays  consist  of 


Line  A 


Line  B 


FIG.  212. 


"polarized"  instruments  with  three  windings,  and  are  operated  by  currents 
induced  in  the  secondary  windings  of  an  induction-coil.  The  primary  wind- 
ing of^each  induction-coil  is  connected  in  series  with  the  line  wire.  One 


244 


AMERICAN  TELEGRAPH  PRACTICE 


winding  of  the  polar  relay  is  serially  connected  with  the  secondary  winding 
of  the  induction-coil.  The  remaining  two  windings  of  the  polar  relay  are 
arranged  differentially  and  serve  as  a  means  of  " locking"  the  relays. 

Two  methods  are  shown  in  the  accompanying  diagrams,  Figs.  211  and  212. 

In  the  arrangement  shown  in  Fig.  211  two  polarized  relays  are  used  with 
each  main  line,  one  relay  serving  to  repeat  the  signals  into  the  opposite 
line,  while  the  other  is  employed  to  lock  the  relay  operated  by  the  opposite 
line. 

Figure  212  shows  a  somewhat  similar  arrangement  employing  one  polar 
relay  and  a  "pony"  relay  in  connection  with  each  main  line  wire.  The 
pony  relay  serves  as  the  means  for  repeating  the  signals  into  the  opposite 
line,  while  the  polar  relay  serves  to  actuate  the  pony  relay  controlling  the 
operation  of  the  opposite  line. 

THE  CATLIN  PERMANENTLY  ADJUSTED  REPEATER 

Another  type  of  repeater  designed  with  the  object  of  securing  immunity 
from  the  effects  of  variations  in  the  electrical  condition  of  lines  is  that  in- 
vented by  Mr.  Fred.  Catlin,  the  theory  of  which  is  illustrated  in  Fig.  213. 


East 


West 


FIG.  213. — Catlin  permanently  adjusted  single-line  repeater. 

It  will  be  noticed  that  the  armature  of  the  relay  stands  in  the  center, 
midway  between  the  line  contacts,  which  means  that  when  the  circuit  is 
idle  there  is  no  current  in  the  main  line  wires.  At  the  distant  western  and 
distant  eastern  stations,  battery  is  applied  to  the  line  only  when  the  signaling 
key  is  closed. 

The  system,  therefore,  will  be  recognized  as  similar  to  the  "open  cir- 
cuit" arrangement,  previously  described  in  connection  with  single  Morse 
lines. 

At  the  repeater  station,  the  relay  employed  is  a  form  of  polarized  instru- 
ment, having  a  double  set  of  contacts  controlled  by  the  movement  of  the 
armature. 


SINGLE-LINE  REPEATERS  245 

Referring  to  Fig.  213 :  When  the  eastern  office  key  is  in  the  open  position 
as  shown,  closing  the  key  at  the  western  office  applies  battery  to  the  main 
line  at  the  latter  station  which  furnishes  current  to  actuate  the  west  coil  of 
'the  relay  at  the  repeater  station.  As  the  armature  A  is  attracted  toward 
the  cores  of  the  west  magnet,  the  contact  at  d  is  opened  and  the  contact  at 
C  is  closed,  thereby  opening  the  ground  connection  through  the  east  coil  of 
the  relay,  and  applying  main-line  battery  to  the  line  east.  Consequently 
the  main-line  relay  at  the  eastern  station  is  closed  in  response  to  the  closed 
key  at  the  western  station.  The  crossarm  represented  by  the  heavy  black 
line  is  made  of  ebonite  or  ivory,  and  is  rigidly  attached  to  the  armature, 
being  so  adjusted  in  length  that  when  the  gap  C  is  closed,  the  gap  d  is  open, 
due  to  the  fact  that  the  lever  L  (ordinarily  held  in  the  closed  position  by  the 
spring  S)  is  pushed  away  from  the  closed  position  by  the  insulated  shaft,  or 
crossarm. 

The  transmission  of  a  signal  from  the  east  to  the  west  would  be  by  the 
reverse  process. 

If  while  the  west  is  sending,  the  eastern  office  desires  to  break,  the  operator 
at  the  latter  office  closes  his  key,  thereby  placing  battery  to  line  which  causes 
the  armature  of  the  relay  at  the  repeater  station  to  apply  battery  to  the  line 
west,  opposing  the  battery  at  the  western  station  and  instantly  interrupting 
the  sender  at  the  latter  station. 

It  is  evident  that  this  repeater  is  practically  independent  of  changes  in 
the  volume  of  line  current,  and  that  no  alterations  in  adjustment  are  neces- 
sary when  the  method  of  transmission,  or  the  character  of  the  signals  is 
changed. 

The  method  is  applicable,  however,  only  in  special  cases,  and  where  the 
open-circuit  system  of  signaling  may  be  worked  satisfactorily. 

NOTES  ON  REPEATER  CONNECTIONS 

In  the  various  repeater  diagrams  given,  in  some  instances  the  local  cir- 
cuits are  shown  as  being  supplied  with  current  from  primary  batteries,  in  other 
cases  a  dynamo  is  shown  as  the  source  of  current.  Also,  in  some  cases  the 
local  batteries  are  shown  connected  as  indicated  in  Fig.  2140,  while  in  other 
cases  grounded  circuits  as  indicated  in  Fig.  2146  are  shown. 

So  far  as  the  operation  of  the  instruments  is  concerned,  it  is  immaterial 
whether  gravity  battery  or  dynamo  current  is  used,  provided  the  required 
current  strengths  are  maintained  in  the  various  circuits.  When  battery  is 
used,  the  internal  resistance  of  the  battery  as  a  whole  (nXr),  in  a  sense, 
serves  as  a  protective  resistance  in  case  of  short  circuits.  When  a  dynamo 
source  of  current  is  employed  it  is  necessary  to  use  resistance  units  in  the 
form  of  coils  of  German  silver,  or  other  high  resistance  wire,  to  protect  the 
dynamos  in  case  of  short  circuit,  and  to  regulate  the  volume  of  current  flowing 
in  each  circuit. 


246 


AMERICAN  TELEGRAPH  PRACTICE 


Local  instruments,  such  as  sounders,  transmitters,  repeating  sounders, 
etc.,  may  be  wound  to  have  resistances  of  4,  10,  20, 40,  or  150  ohms,  generally 
depending  upon  the  current  strengths  upon  which  they  are  to  be  operated 
(see  Appendix  D.).  The  available  e.m.f.,  for  local  battery  purposes, ' 
varies  in  different  installations,  and  may  be  2,  4,  6,  26,  40,  52,  or  no  volts. 

With  a  given  e.m.f.,  and  a  given  current  requirement,  the  value  of  the 
regulating  resistance  in  a  given  instance  may  be  ascertained  by  means  of 

Ohm's  law  (R  =  y  j ,  always  taking  into  consideration  the  resistance  of  the  in- 
strument to  be  operated. 

In  the  interests  of  economy,  in  many  instances  the  local  commercial  110- 
volt  direct-current  is  availed  of  for  battery  purposes.     In  which  case  where 


FIG.  214. 

i5o-ohm  local  instruments  (sounders,  transmitters,  etc.)  are  used,  it  is  usual 
to  employ  resistance  units  of  1,500  or  2,000  ohms  in  series  with  each 
instrument. 

In  regard  to  Figs.  2140  and  2146,  it  is  immaterial  which  method  is  availed 
of  so  far  as  current  values  are  involved.  Obviously,  though,  the  ground 
return  arrangement  (2140)  makes  possible  a  greatly  reduced  number  of  indi- 
vidual connections,  and  a  correspondingly  reduced  number  of  conducting 
wires. 


REPEATER  ADJUSTMENTS 

In  the  operation  of  repeaters,  it  is  important  to  see  that  all  binding-post 
connections  are  secure  and  that  circuit  contact-points  are  kept  bright  and 
clean.  The  armatures  of  transmitters  and  repeating  sounders  should  be 
adjusted  to  have  as  little  play  as  possible  and  still  permit  of  clear  "breaks" 
and  insure  firm  and  positive  "make"  contact.  This  reduces  to  a  minimum 
the  losses  due  to  the  mechanical  inertia  of  the  comparatively  heavy  moving 
parts  of  the  instrument,  and  makes  for  more  regular  performance,  and  higher 
speeds. 


SINGLE-LINE  REPEATERS  247 

When  a  repeater  set  has  been  properly  adjusted,  it  does  not  follow  that 
the  circuit  made  up  through  it  will  at  all  times  be  satisfactorily  operative. 
That  this  is  so  is  not  necessarily  a  reflection  on  the  repeater,  as  in  most  cases 
the  trouble  which  develops  is  primarily  due  to  changes  in  the  weather 
conditions  along  the  line,  thus  causing  changes  in  the  electrical  conditions 
obtaining  in  the  main-line  circuits  outside  of  the  repeater.  Ordinarily  these 
changes  should  be  met  by  means  of  the  magnet  adjusting  screw,  moving  the 
magnets  closer  to,  or  farther  away  from  the  armature  as  may  be  necessary. 
If  the  retractile  springs  of  relays  have  a  tension  sufficient  to  withdraw  the 
armatures  when  the  current  in  the  magnet  windings  has  fallen  to  a  compara- 
tively low  value  very  little  can  be  gained,  but  often  much  harm  is  done  by 
giving  the  spring  adjustment  too  much  attention. 

The  main-line  contacts  if  well  cleaned,  and  set  close,  with  all  lock-screws 
tight,  should  not  have  to  be  changed  unless  excessive  sparking  occurs.  The 
latter  condition  may  indicate  that  the  points  have  become  dirty,  or  that  an 
unnecessarily  large  amount  of  battery  is  applied  to  the  circuit. 

When  the  armature  of  a  transmitter  is  held  in  the  closed  position,  there 
should  be  a  space  of  at  least  10  mils  (o.oio  in.)  between  the  armature  and  the 
pole-faces  of  the  magnets.  This  may  be  determined  by  drawing  a  sheet  of 
ordinary  message  or  writing  paper  between  the  armature  and  the  pole  faces 
while  the  lever  is  held  tightly  closed,  preferably  by  magnetizing  the  cores. 

In  the  working  of  repeaters  a  troublesome  "kick"  occasionally  develops, 
the  cause  of  which  is  not  always  easy  to  locate,  and  unless  the  attendant  in 
charge  of  the  repeater  has  been  properly  trained  and  instructed,  or  has  had 
sufficient  experience  in  the  handling  of  repeaters  to  enable  him  to  quickly 
locate  the  trouble,  a  repeater  set  may  be  thrown  out  as  unworkable  when  in 
reality  there  is  nothing  wrong  except  incorrect  adjustment. 

With  any  of  the  standard  forms  of  repeater  herein  described,  when  a 
"kick"  develops,  the  cause  which  produces  it  may  be  run  down  by  the 
following  method.  First,  open  the  line  key  at  the  repeater  station  which 
controls  one  of  the  main-line  circuits;  say  that  the  eastern  circuit  is  selected. 
Then,  with  the  hand,  close  and  open  at  intervals  the  armature  of  the  relay 
which  is  open.  It  should  then  be  noted  whether  the  kick  appears  when  the 
relay  armature  makes  contact  with  its  front-stop,  or  when  the  armature  is 
moved  away  from  that  point.  If  the  kick  is  in  evidence  when  the  relay 
closes,  the  indications  are  that  the  relay  in  circuit  with  the  opposite  line  (in 
this  case  the  west  relay)  does  not  act  quickly  enough  to  maintain  the  closed 
position  of  the  transmitter  armature  at  the  instant  the  holding  coil,  or 
repeating  sounder  "lets  go"  in  response  to  the  closing  of  the  opposite  trans- 
mitter. In  the  case  of  the  Weiny-Phillips  repeater  this  means  that  there  is 
too  great  an  interval  of  time  elapsing  between  the  instant  the  holding  coil 
of  the  relay  releases  the  armature,  and  the  instant  the  main-line  coils  of  the 
same  relay  "  take  hold  "  of  the  armature.  The  cause  may  be  that  the  tongue 


248  AMERICAN  TELEGRAPH  PRACTICE 

of  the  transmitter  does  not  close  the  main-line  circuit  at  an  instant  coincid- 
ing closely  enough  with  that  at  which  current  is  made  to  flow  differentially 
through  the  windings  of  the  holding  coil  of  the  relay.  This  means  that 
the  holding  coil  releases  the  armature  before  the  main-line  coils  have  become 
magnetized,  and  this  interval  although  brief  may  cause  a  kick  of  the  arma- 
ture of  the  opposite  transmitter.  If  it  is  found  that  the  transmitter  adjust- 
ment is  correct,  the  trouble  may  be  due  to  the  main-line  coils  of  the  relay 
being  pulled  back  too  far  in  a  direction  away  from  the  armature.  In  either 
case  the  remedy  is  proper  adjustment.  If  the  kick  is  in  evidence  at  the 
instant  that  the  relay  armature  is  moved  away  from  the  front  stop  the  cause 
will  likely  be  found  to  be  tardy  action  of  the  repeating  sounder,  holding 
magnet,  or  other  holding  device.  In  which  case  the  trouble  (in  the  case  of 
the  Atkinson  repeater)  may  be  eliminated  by  lifting  the  armature  of  the  re- 
peating sounder  a  trifle,  or  by  giving  the  spring  a  greater  tension.  If  the 
set  in  trouble  is  of  the  Weiny-Phillips  pattern,  moving  the  holding  coil 
closer  to  the  relay  armature,  will  in  most  cases  eliminate  the  kick  which 
develops  when  the  relay  armature  is  moved  away  from  the  closed  contact. 

Should  the  kick  appear  in  the  other  half  of  the  set,  its  cause  may  be 
located  by  the  process  the  reverse  of  that  just  described;  that  is,  by  manipu- 
lating the  armature  of  the  west  relay,  for  the  purpose  of  determining  whether 
the  kick  appears  when  the  relay  armature  is  moved  into  contact  with,  or 
away  from  the  front-stop. 


CHAPTER  XIII 
DUPLEX  TELEGRAPHY 

By  duplex  telegraphy  is  meant  a  system  which  makes  possible  the  trans- 
mission of  two  messages  over  a  single  wire  at  the  same  time,  one  in  each 
direction. 


THE  SINGLE-CURRENT  DUPLEX 

The  more  important  elements  of  the  single-current  duplex  arc  the  trans- 
mitter, the  differential  relay,  the  artificial-line  rheostat,  and  the  condenser. 

The  single-current  duplex  is  sometimes  referred  to  as  the  Stearns  duplex 
in  honor  of  the  inventor,  Mr.  Joseph  B.  Stearns. 

In  single  Morse  circuits,  such  as  those  described  in  Chapter  VII,  the 
armatures  of  all  relays  in  the  circuit,  including  that  at  the  home  station 

A  B 


FIG.  215. — Single-current,  or  Stearns  differential  duplex. 

and  that  at  the  distant  station,  are  operated  simultaneously  when  any  signal- 
ing key  connected  into  the  circuit  is  manipulated. 

When  it  is  required  to  transmit  a  message  in  each  direction  over  a  line 
simultaneously,  it  is  evident  that  the  receiving  relay  at  each  of  the  two 
terminal  stations  must  respond  to  the  manipulations  of  the  signaling  key 
at  the  distant  station,  and  not  to  the  operation  of  the  key  at  the  home 
station. 

Figure  215  is  a  diagram  of  the  theoretical  connections  of  the  single-cur- 
rent duplex.  A  line  is  shown  extending  between  stations  A  and  B.  T  and 
T'  are  the  transmitters,  DR  and  DR'  the  differential  relays,  AR  and  AR' 
the  artificial-line  rheostats,  and  b  and  b'  the  main-line  batteries  at  A  and  B 

249 


250  AMERICAN  TELEGRAPH  PRACTICE 

respectively.  The  function  of  the  transmitter  is  simply  that  of  a  signaling 
key  connected  into  the  main-line  circuit  in  such  a  manner  that  when  the 
key  is  closed  battery  is  appllied  to  the  line,  and  when  the  key  is  opened 
the  line  is  grounded. 

Figure  216  shows  a  key  connected  into  the  main-line  circuit  direct,  to 
do  the  work  of  a  transmitter.  Here,  as  in  the  case  of  the  transmitter  shown 
in  Fig.  215,  it  is  apparent  that  when  the  key  is  depressed,  battery  is  applied 
to  the  line,  and  when  the  key  is  opened  the  line  is  grounded. 

In  the  operation  of  duplexes — as  will  be  explained  more  fully  later  on — 
it  is  essential  that  in  the  operation  of  the  transmitter  or  of  the  key,  the 
shortest  possible  interval  of  time  shall  elapse  between  the  instant  battery 
is  removed  from  the  main  line,  and  the  instant  the  ground  connection  is 


1 


FIG.  216. — Showing  an  ordinary  Morse  key  taking  the  place  of  the  transmitter  in  a  single- 
current  duplex. 

substituted  therefor.  Obviously  if  an  ordinary  key  were  used  to  control 
the  application  of  battery  and  removal  of  ground  connection,  and  vice 
versa,  in  the  act  of  signaling;  the  lapse  of  time  between  these  two  contacts 
would  be  excessive,  due  to  the  comparatively  slow  movement  of  the  hand 
in  working  the  key;  being  more  pronounced  the  wider  the  gap  maintained 
between  the  contacts  of  the  key.  Also,  were  the  ordinary  key  used  directly 
in  the  line  circuit,  the  speed  of  operation  would  be  considerably  curtailed 
owing  to  the  requirement  imposed  upon  the  operator  to  make  equally  firm 
and  solid  contact  between  the  key-lever  and  the  ground  connection  as  be- 
tween the  lever  and  the  battery  contact;  a  condition  that  the  average 
operator -would  find  quite  difficult  to  meet. 

The  transmitter,  therefore,  is  used  for  the  purpose  of  insuring  instan- 
taneous transfer  of  the  line  connection  from  battery  contact  to  ground 
contact  in  response  to  the  operation  of  the  key  which  controls  the  operation 
locally,  of  the  transmitter,  regardless  of  whether  the  key  is  operated  rapidly 
or  slowly. 

By  noting  the  construction  of  the  transmitter  shown  in  connection  with 
the  diagram,  Fig.  215,  it  may  be  seen  that  the  moving  element  of  the  instru- 
ment may  be  so  adjusted  that  at  the  instant  the  battery  is  removed,  the 


DUPLEX  TELEGRAPHY  251 

ground  contact  is  made,  and  thus  the  continuity  of  the  line  is  preserved,  or 
in  other  words,  the  period  during  which  the  line  is  open  is  reduced  to  a 
minimum.  This  is  a  requirement  of  considerable  consequence  in  the  oper- 
ation of  multiplex  telegraphs. 

THE  DIFFERENTIAL  RELAY 

If  the  reader  will  review  what  was  stated  in  Chapter  X,  page  155,  in 
regard  to  the  differential  galvanometer,  and  in  Chapter  XII,  page  224,  dealing 
with  the  differentially  wound  holding  magnet  of  the  Weiny-Phillips  repeater 
relay,  he  will  be  better  prepared  to  understand  the  construction  of  and  the 
operation  of  the  differential  relay  used  in  connection  with  duplex  and  quad- 
ruplex  telegraphs. 

All  that  is  required  is  that  when  currents  of  equal  strength  pass  through 
both  windings  of  the  differential  magnet,  the  cores  shall  not  become  magnet- 
ized. It  is  to  be  remembered,  however,  that  the  amount  of  magnetism  pro- 
duced in  either  core  is  directly  dependent  upon  the  strength  of  current  flow- 
ing in  the  winding  around  the  core,  and  if  the  magnetic  effect  produced  by 
one  of  the  coils  is  to  be  exactly  neutralized  by  that  of  the  other,  it  is  essential 
that  the  current  strength  in  the  two  coils  be  equal. 

If  the  current  strength  in  one  coil  is  greater  than  that  in  the  other  coil, 
naturally  the  excess  current  produces  a  certain  amount  of  magnetism  which 
is  not  neutralized,  and,  due  to  this  magnetism,  the  armature  of  the  relay  is 
attracted. 

In  an  earlier  chapter  it  was  explained  that  the  strength  of  the  current 
flowing  in  a  circuit  is  dependent  upon  the  value  of  the  applied  e.m.f.  and 
upon  the  ohmic  resistance  of  the  cir-  pOQU  u 

cuit.     In   the   case   of  the  differential  s    /*&& 

relay,  therefore,  it  is  essential  that  if      I  XJlfl^ry 

the  relay  is  to  be  truly  differential,  the   -=-  zo°w    I  goou 

current  strength  in  both  windings  must 

be  identical,  and  this  in  turn  imposes    _ L  — j— 

the  requirement  that  the  resistance  of 

_  FIG.  217. 

each  circuit  must  be  identical. 

Suppose  a  differential  relay  having  a  resistance  of  200  ohms  in  each  wind- 
ing is  connected  with  a  source  of  e.m.f.  so  that  current  flows  through  both 
coils  as  indicated  in  Fig.  217.  If  it  is  required  that  the  cores  of  the  relay 
magnets  shall  not  be  magnetized,  it  is  necessary  that  equal  current  values 
obtain  in  each  of  the  divided  paths  to  ground.  The  fact  that  the  resistance 
of  each  of  the  relay  coils  is  the  same  is  of  little  consequence  unless  the  circuits 
beyond  the  relay  also  are  of  equal  resistance. 

In  Fig.  217,  current  passes  through  one  coil  of  the  relay  and  beyond 
through  a  line  wire  having  1,000  ohms  resistance,  thence  to  ground.  The 


252  AMERICAN  TELEGRAPH  PRACTICE 

other  coil  of  the  relay  forms  a  portion  of  a  path  to  ground  through  a  resist- 
ance coil  of  800  ohms.  It  is  evident,  therefore,  that  as  the  current  divides 
at  S  it  has  two  paths  to  ground,  one  having  a  resistance  of  1,000  ohms  and 
the  other  a  resistance  of  1,200  ohms,  and  it  is  apparent  that  there  will  be  more 
current  flowing  in  the  circuit  having  less  resistance  than  in  the  other.  As  a 
consequence,  one  core  of  the  relay  is  to  a  certain  extent  magnetized  due  to 
the  extra  current  in  one  coil  of  the  relay  over  that  in  the  other  coil. 

A  B  The  resistance  of  main-line  wires 

varies  from  a  few  hundred  ohms  to 


/*&?>- 


Line  200  Miles 


1000  Ohms 


AL 


1000 
Ohms 


several  thousand  ohms  and  where 
differential  relays  are  used  in  duplex 
operation,  in  order  to  insure  that 
equal  current  values  obtain  in  each 
coil  of  the  relay  when  the  home  bat- 
tery is  applied  to  the  line  and  the 

FIG.  218.— Resistance  of  the  artificial  line  distant  end  of  the  line  is  grounded, 
balancing  the  resistance  of  the  line  wire  to  it  is  necessary  to  have  at  the  home 
distant  station.  ,.  , .  A  ,  . 

station     an     adjustable     resistance 

through  which  the  other  coil  of  the  relay  may  be  connected  to  ground. 

Obviously  if  this  resistance  is  adjusted  to  have  a  value  equal  to  that  of 
the  line  wire  to  the  distant  station,  like  current  values  will  exist  in  both 
coils  of  the  relay  and  there  will  not  be  any  magnetism  produced  in  the  cores 
of  the  relay. 

The  adjustable  resistance  used  to  equate  the  resistance  of  the  main-line 
wire  is  generally  called  the  artificial  line,  Fig.  218. 


THE  ARTIFICIAL  LINE 

As  has  been  pointed  out  elsewhere  in  this  work,  all  line  wires  possess 
electrostatic  capacity.  The  quantity  of  electric  charge  accumulated  upon 
the  surface  of  the  conductor  depends  upon  the  superficial  area  of  the  con- 
ductor, upon  the  distance  intervening  between  the  conductor  and  the  earth 
(or  between  the  conductor  concerned  and  other  conductors  in  electrical 
contact  with  the  earth),  and  upon  the  nature  of  the  insulating  medium  inter- 
vening between  the  line  wire  and  the  earth.  In  any  line  of  considerable 
length,  a  portion  of  the  current  is  bound  up  in  the  form  of  static  charge. 

The  first  rush  of  current  into  the  line  at  the  instant  the  battery  is  applied 
thereto,  (sometimes  referred  to  as  the  current  of  charge)  for  an  instant  pro- 
duces a  much  greater  magnetic  effect  upon  the  armature  of  the  home  relay, 
than  obtains  when  the  entire  line  has  been  fully  charged  and  permanent  con- 
ditions established  in  the  circuit. 

The  result  of  the  initial  inrush  of  current,  greatly  exceeding  in  volume,  as 
it  does,  the  final  current,  is  that  a  false  signal  or  "kick"  of  the  relay  ar- 


DUPLEX  TELEGRAPHY  253 

mature  is  produced.  The  energy  of  the  kick  depends  upon  the  electrostatic 
capacity  of  the  line,  being  greater  where  the  capacity  is  high,  and  less  pro- 
nounced as  the  static  charge  taken  on  by  the  line  wire  is  less. 

Also,  there  is  to  be  considered  the  effect  of  static  discharge  which  occurs 
at  the  instant  the  line  wire  is  shifted  from  the  battery  connection  to  the  ground 
connection  upon  opening  the  key  controlling  the  operation  of  the  trans- 
mitter. At  this  instant  the  electrostatic  charge  which  has  been  accumulated 
upon  the  surface  of  the  conductor  flows  back  to  ground  by  way  of  the  ground 
contact  of  the  transmitter,  passing  through  the  main-line  coil  of  the  differen- 
tial relay,  again  producing  a  kick  of  the  relay  armature. 

In  view  of  these  considerations,  therefore,  it  is  necessary  if  the  false 
signals  which  are  produced  at  the  beginning  and  the  end  of  each  intended 
signal  are  to  be  neutralized  or  nullified,  that  the  artificial  line  be  made  to 
possess  properties  identical  with  those  of  the  main-line  wire,  i.e.,  resistance 
and  capacity. 

The  application  of  the  electric  condenser  as  an  adjunct  of  the  artificial 
line  gives  to  the  latter  the  desired  property  of  electrostatic  capacity. 

A  condenser  path  to  ground  via  the  artificial-line  coil  of  the  differential 
relay  results  in  an  initial  rush  of  current  through  that  coil  at  the  instant 
battery  is  applied  to  the  line,  which,  by  means  of  adjustable  ''timing" 
resistances  in  series  therewith  may  be  made  to  exactly  equal  in  strength  and 
duration,  the  corresponding  rush  of  current  which  takes  place  at  the  same 
instant  through  the  main-line  coil  of  the  relay,  thus  at  the  critical  moment 
insuring  identical  current  values  in  both  coils  of  the  relay. 

And,  further,  when  the  line  wire  is  shifted  from  battery  contact  to  the 
ground  connection  at  the  moment  the  key  is  opened,  the  discharge  from  the 
condenser  associated  with  the  artificial  line  takes  place  through  the  relay 
coil  forming  a  portion  of  the  artificial-line  circuit  at  the  same  instant  that 
the  main  line  discharges  through  the  relay  coil  forming  a  portion  of  the  main- 
line circuit,  thus  again  at  the  critical  moment  insuring  equal  current  values 
in  the  two  coils. 

.To  understand  the  import  of  the  above  remarks,  one  must  have  in  mind 
the  positions  of  the  main-line  circuit  and  of  the  artificial-line  circuit  through 
the  windings  of  the  respective  relay  coils,  also  that  the  magnet  made  up  by 
the  artificial-line  relay  coil,  and  the  magnet  made  up  by -the  main-line  relay 
coil  both  control  the  same  armature. 

When  the  relay  is  operated  by  current  from  the  distant  station  its  opera- 
tion is  due  to  a  surplus  of  current  in  the  main-line  coil  over  what  may  be  in 
the  artificial-line  coil  of  the  relay. 

When  the  signaling  keys  at  each  end  of  the  line  are  closed  and  like  poles 
of  battery  are  applied  at  both  ends  of  the  line,  the  desired  signal  is  made  by 
the  home  battery  on  the  home  relay,  and  is  the  result  of  a  surplus  of  current 
in  the  artificial-line  coil  of  the  relay  over  what  may  be  in  the  main-line  coil. 


254 


AMERICAN  TELEGRAPH  PRACTICE 


When,  due  to  electrostatic  charge  or  discharge  of  the  main  line  the  current 
in  the  main-line  coil  of  the  relay  is  augmented  above  that  traversing  the 
artificial-line  coil  of  the  relay,  a  false  signal  will  be  produced  unless  at  that 
instant  the  current  flowing  in  the  artificial-line  side  of  the  relay  is  increased 
to  an  equal  value.  This  is  what  is  accomplished  by  using  condensers  and 
retardation  resistance  coils  in  connection  with  the  artificial  line. 

Figure  219  shows  the  theoretical  arrangement  of  the  artificial-line  circuits. 
On  the  right  is  shown  three  adjustable  resistance  groups  used  in  balancing 
the  "ohmic"  resistance  of  the  main-line  wire.  With  the  values  shown  it  is 
possible  to  avail  of  resistances  ranging  from  10  ohms  to  11,100  ohms,  variable 
within  steps  of  10  ohms. 


Main  Line 


Ten 
1000  Ohm  Steps 


FIG.  219. — Circuits  of  the  artificial  line,  showing  the  adjustable  resistance  on  the  right  and 
the  condensers  and  condenser  timing  resistances  on  the  left. 

On  the  left,  two  adjustable  electric  condensers  C1  and  C2  are  shown, 
each  having  a  maximum  capacity  of  3  microfarads.  Each  condenser  has 
in  series  with  it  an  adjustable  resistance  (see  Timing  the  Condenser 
Discharge). 


DOUBLE -CURRENT  DUPLEX  SYSTEMS 

As  a  result  of  the  development  of  more  efficient  and  satisfactory  duplex 
systems,  the  single-current  duplex  is  rarely  used  in  this  country,  except  where 
it  is  combined  with  the  polar  duplex  in  forming  the  differential  quadruplex 
system  of  telegraphy  by  means  of  which  two  messages  are  sent  in  each 
direction  over  a  single  wire,  simultaneously. 

Further  treatment  of  the  single-current  duplex  will  be  deferred  until  it  is 
considered  as  a  component  part  of  the  quadruplex. 


DUPLEX  TELEGRAPHY  255 

THE  POLAR  DUPLEX 

The  essential  elements  of  the  polar  duplex  are  a  battery  pole-changer, 
a  differentially  wound  polarized  relay,  an  artificial  line  rheostat,  and  an 
artificial  capacity. 

THE  POLE-CHANGER 

The  transmitter  shown  in  connection  with  the  single-current  duplex, 
Fig.  215,  has  connected  to  one  of  its  contacts  the  positive  pole  of  a  main- 
line battery  and  to  the  other  contact  a  circuit  to  ground.  If  to  the  latter  tne 
negative  pole  of  a  main -line  battery  were  connected  instead  of  the  ground 
wire,  closing  the  signaling  key  would  send  to  line  a  positive  impulse,  and 
opening  the  key  would  send  to  line  a  negative  impulse,  in  which  case  the  trans- 
mitter might  correctly  be  regarded  as  serving  as  a  pole-changer,  inasmuch  as 
the  polarity  of  the  battery  placed  in  contact  with  the  line  wire  changes 
from  positive  to  negative  and  vice  versa  each  time  the  transmitter  tongue 
is  caused  to  break  contact  with  the  positive  battery  terminal  and  make 
contact  with  the  negative  battery  terminal. 

"  When  dynamo  currents  were  introduced  in  the  operation  of  telegraph 
lines  it  was  found  that  the  form  of  transmitter  here  considered,  and  which 
had  previously  answered  the  requirements  where  gravity  batteries  were 
universally  employed  in  telegraph  work,  failed  to  give  satisfactory  results 
owing  to  the  momentary  short  circuit  which  exists  when  the  line  contact 
is  shifted  from  the  lever  to  the  tongue  of  the  transmitter,  and  again  when  the 
opposite  movement  takes  place,  in  the  act  of  signaling.  Irr*  the  Stearns 
duplex  the  resistance  presented  to  the  individual  battery  used,  was,  at  the 
instant  the  transfer  of  contact  took  place,  made  approximately  equal  to  that 
of  the  total  internal  resistance  of  the  battery.  When  the  dynamo  with  its 
negligible  internal  resistance  is  applied  to  the  operation  of  the  polar  duplex, 
two  machines  of  equal  potential  and  of  opposite  polarity  are  separately  con- 
nected to  the  contacts  between  which  plays  the  armature  tongue  carrying 
the  main-line  contact.  At  the  instant,  therefore,  that  the  transfer  of  con- 
tact takes  place  unless  there  is  an  appreciable  length  of  air-gap  main- 
tained between  the  opposing  battery  terminals,  there  will  be  established 
a  momentary  short  circuit  between  the  two  dynamos  (where  two  2oo-volt 
machines  are  employed  this  amounts  to  an  aggregate  potential  of  400  volts) 
which  might  result  in  serious  damage  to  the  machines.  Even  where  arti- 
ficial resistances  are  inserted  in  series  with  each  machine,  excessive  spark- 
ing occurs  when  the  line  contact  is  shifted  from  one  pole  to  the  other. 

The  introduction  of  the  double-current  duplex  called  for  the  substitution 
of  a  transmitter  in  place  of  the  type  of  instrument  used  with  the  single-current 
duplex,  which  would  meet  the  changed  conditions. 


256 


AMERICAN  TELEGRAPH  PRACTICE 


The  new  form  of  transmitter,  or  pole-changer  as  it  has  since  been  called, 
provides  for  the  maintenance  of  ah  air-gap  as  the  main-line  contact  is  shifted 
from  one  pole  of  the  battery  to  the  other. 

One  form  of  pole-changer  employed  by  one  of  the  commercial  telegraph 
companies,  is  that  known  as  the  walking-beam  pattern,  see  Fig.  220. 

Another  type  of  pole-changer  extensively  employed  is  that  illustrated  in 


To  Line 


FIG.  220. — Walking-beam  pattern 
of  pole- changer. 


FIG.  221 . — Double-contact  relay  type  of  pole- 
changer. 


Fig.  221,  which  will  be  recognized  as  a  simple  double-contact  relay  form  of 
instrument,  a  photographic  view  of  which  is  shown  in  Fig.  222. 

With  either  of  these  instruments,  it  is  evident  that  connection  cannot 
be  made  between  the  line  and  one  dynamo  until  contact  has  first  been  broken 
between  the  line  (the  lever)  and  the  other  dynamo  connection. 


FIG.  222. — Pole-changer. 

So  far  as  the  polar  duplex  is  concerned,  the  same  necessity  does  not  exist 
for  the  employment  of  a  continuity-preserving  transmitter  as  was  the  case 
with  the  single-current  duplex,  the  reason  for  which  will  be  explained 
presently. 

The  combination  of  the  polar  duplex  with  the  Stearns  duplex,  in  forming 
the  differential  quadruplex,  transferred  to  the  latter  the  alternative  of  using 


DUPLEX  TELEGRAPHY  257 

on  the  single-current  half  of  the  system  a  continuity-preserving  transmitter, 
or  a  pole-changer  type  of  transmitter  which  at  all  times  maintains  a  small 
air-gap  between  the  opposing  dynamo  terminals.  From  what  has  been 
stated  in  regard  to  the  possibility  of  short  circuits  where  the  continuity- 
preserving  instrument  is  used  in  connection  with  dynamo  machines,  it  is 
apparent  that  the  employment  of  the  latter  mentioned  instrument  is  not 
practicable.  In  practice,  therefore,  it  is  customary  to  use  an  open-gap  trans- 
mitter on  the  single-current  side  of  the  quadruplex,  similar  to  that  used  on 
the  double-current  side. 

In  the  operation  of  the  single-current  side  of  the  quadruplex,  the  objec- 
tions previously  mentioned  in  connection  with  the  employment  of  the  air-gap 
transmitter  in  Stearns  duplex  operation,  still  exist,  as  it  is  evident  that  there 
are  constantly  recurring  periods  of  "insufficient  current"  while  the  lever  of 
the  transmitter  (to  which  the  line  conductor  is  connected)  is  traveling  from 
one  battery  contact  to  the  other  in  the  act  of  signaling. 

Inasmuch,  however,  as  the  employment  of  the  open-gap  transmitter  is 
imperative,  it  has  been  necessary  to  avail  of  other  means  of  bridging  over 
these  periods,  and  to  employ  circuit  accessories  which  act  to  prevent,  or  at 
least  to  minimize  the  tendency  to  produce  false  signals  on  the  reading  sounder 
operated  by  the  receiving  relay  on  the  single-current  side  of  the  quadruplex. 
These  accessories  are  variously  referred  to  as  "bug-traps,"  " uprighters, " 
etc.,  and  their  application  and  action  will  be  described  in  connection  with 
quadruplex  systems. 


THE  "  POLAR"  RELAY 

All  of  the  inherent  difficulties  experienced  in  the  operation  of  single 
Morse  lines,  are  encountered  in  the  operation  of  the  single-current  differential 
duplex  system. 

During  favorable  weather  and  where  a  high  degree  of  line  insulation  is 
maintained,  both  of  these  methods  of  telegraphy  are  satisfactory.  But, 
when,  due  to  excessive  leakage  conductance  the  current  values  at  the  re- 
ceiving end  are  low,  considerable  difficulty  is  experienced  in  maintaining 
satisfactory  operation. 

The  polar  duplex  overcomes  this  difficulty  to  a  great  extent,  and  by  means 
of  this  system  lines  may  be  worked  satisfactorily  long  after  adverse  "weather 
conditions  have  rendered  single  Morse,  and  single-current  duplex  systems 
inoperative. 

Figure  223  shows  a  theoretical  view  of  the  magnetic  circuit  of  the  polar 
relay. 

It  will  be  seen  that  the  windings  are  identical  with  those  of  the  ordinary 
single-current  differential  relay.  Current  from  the  battery  flows  through 

17 


258 


AMERICAN  TELEGRAPH  PRACTICE 


Line 


the  windings  in  opposite  directions,  the  action  of  one  coil  neutralizing  that 
of  the  other,  the  result  of  which  is  that  the  core  is  not  magnetized  so  far  as 
any  action  due  to  the  current  from  the  battery  is  concerned. 

The  fundamental  difference  between  the  two  instruments  is  that  in  the 
polar  relay  the  tongue  is  held  on  either  side  due  to  the  magnetic  pull  of  the 
permanent  magnet  which  constitutes  the  cores  of  the  electromagnets. 

In  the  case  of  the  common  differ- 
ential relay  the  armature  tongue  is 
held  in  the  closed  position  by  the 
action  of  either  or  both  magnet  coils, 
and  in  the  open  position  by  the  action 
of  a  retractile  spring  which  with- 
draws the  armature  from  the  closed 
position  when  the  coils  are  not  ener- 
gized. The  armature  of  the  polar 
?%'Li'ne  relay  is  held  in  the  closed  position 
and  in  the  open  position  by  the  at- 
•i-  -i-  traction  of  one  pole  of  the  permanent 

FIG.  223.-Theory  of  the  differential  polar-  magnet,  and  it  is  necessary  of  course 
ized  relay.  that    the   armature  be  drawn  into 

contact  with  the  open  or  the  closed 

pole  due  to  magnetism  in  the  cores,  resulting  from  the  action  of  current  in 
either  coil  of  the  instrument.  The  important  feature  is  that  after  the  arma- 
ture has  once  been  attracted  toward  either  contact,  it  will  remain  there  whether 
current  remains  in  the  coil  winding  or  not  (provided  there  is  no  current  in 
the  opposite  coil). 

Referring  to  Fig.  223 :  When  the 
key  K  is  operated,  the  armature 
lever  of  the  pole-changer  is  caused 
to  make  contact,  first  with  the 
negative  battery  terminal  and 
then  with  the  positive  battery 
terminal.  If  the  ohmic  resist- 
ances of  the  real  line  and  the 
artificial  line  are  equal,  current 
from  whichever  dynamo  is  con- 
nected with  the  armature  lever 
will  go  through  the  companion 
windings  of  the  relay  differentially, 
with  the  result  that  there  is  no  electromagnetism  produced  in  the  cores 
facing  the  relay  armature.  It  matters  not  whether  the  out-going  current 
is  from  a  positive  source  or  from  a  negative  source:  owing  to  the  fact  that  it 
passes  through  the  windings  of  the  relay  differentially  there  will  be  no  mag- 


FIG.  224. — Permanent   magnet   and  armature 
suspension  of  the  Siemens  polar  relay. 


DUPLEX  TELEGRAPHY 


259 


netism  produced,  and  this,  irrespective  of  the  polarity  of  the  current  flowing 
in  the  circuit. 

If  the  key  K  is  manipulated,  there  will  be  sent  out  a  series  of  impulses 
alternating  in  sign,  from  positive  to  negative  each  time  the  key  is  closed  and 
opened,  and  if  the  resistance  of  the  artificial  line  side  of  the  relay  balances 
that  of  the  line  side,  the  armature  of  the  relay  will  not  be  affected.  More- 
over, it  will  be  found  that  if  the  relay  tongue  is  moved  by  hand  into  contact 
with  its  closed  contact  or  with  its  open  contact,  it  will  still  remain  passive 
to  the  out-going  reversals  from  the  pole-changer. 

In  one  of  the  older  standard  patterns  of  polar  relay,  which  is  known  as 
the  Siemens,  or  " camel-back"  relay,  Fig.  224,  a  comparatively  large  per- 
manent magnet  has  mounted  on  one  end  two  cross-pieces  made  of  soft 
iron  which  form  the  cores  C  and  C'  of  the  main-line  and  artificial-line  coils. 
From  the  other  extremity  of  the  permanent  magnet  the  armature  A  is  sus- 
pended, being  pivoted  in  a  brass  casing,  that  is,  it  is  pivoted  in  bearings, 
which,  being  non-magnetic,  introduce  a  gap  between  the  pole-face  of  the  large 
permanent  magnet  and  the  armature.  The  latter  is  magnetized  inductively 
across  the  existing  air-gap,  to  a  degree  sufficient  to  create  the  desired  attrac- 
tion between  the  free  end  of  the  armature  and  the  cores  of  the  magnets,  both 
of  which  are  of  identical  polarity,  and  opposite  to  that  of  the  extremity  of 
the  permanent  magnet  at  which  the  armature  is  pivoted.  In  the  completed 
instrument,  the  cores  C  and  C',  carry  the  coil  windings  of  the  main-line  mag- 
net and  the  artificial-line  magnet  respectively.  If  it  is  assumed  that  the 
end  B  of  the  permanent  magnet  at  which  the  armature  is  pivoted  is  the  north 
pole,  then  the  free  end  of  the  armature  is  also  of  north  polarity,  and,  owing 
to  the  fact  that  both  cores,  of  the  electro- 
magnets are  attached  to  the  south  pole  of 
the  permanent  magnet,  and  taking  that 
polarity,  it  is  evident  that  the  armature  will 
cling  to  whichever  core  it  may  be  placed  in 
contact  with.  That  is,  it  will  cling  to  either 
the  open  contact,  or  to  the  closed  contact 
when  no  current  traverses  the  windings  of 
the  electromagnets,  or  when  current  flows 
through  the  windings  differentially. 

The  magnets  of  polar  relays  are  usually  so  wound  that  when  current 
from  the  distant  station  flows  through  the  main-line  coil,  it  is  given  a  path 
through  an  auxiliary  winding  in  the  opposite  coil,  in  the  reverse  direction 
(Fig.  225),  which  results  in  the  permanent  induced  magnetism  in  one  of  the 
cores  being  neutralized,  while  the  magnetism  existing  in  the  other  core  is 
intensified,  causing  the  armature  to  be  attracted  toward  the  opposite  con- 
tact. The  reverse  action  takes  place  when  the  battery  poles  at  the  home 
station  and  at  the  distant  station  are  in  opposition  (like  poles  to  line)  in 


FIG.  225. — Coil    windings    of 
differential  polarized  relay. 


260  AMERICAN  TELEGRAPH  PRACTICE 

which  case  the  artificial-line  coil  of  the  home  relay  has  its  magnetism  in- 
creased, and  the  line  coil  has  its  magnetism  neutralized.  Thus,  due  to  the 
action  of  the  current  in  the  coils,  the  armature  is  caused  to  move  into  con- 
tact with  the  open  or  the  closed  contact  as  desired. 

The  office  of  the  auxiliary  winding  in  each  case  is  to  act  as  a  "  clearing 
out"  agency. 

There  are  several  distinct  types  of  polar  relay  used  by  the  various  tele- 
graph administrations,  each  relay  having  its  peculiarities  of  design,  but  the 
principle  upon  which  all  polar  relays  operate  is  the  same. 

Figure  226  illustrates  the  form  of  polar  relay  used  by  the  Postal  Tele- 
graph-Cable Company.  It  differs  from  the  type  of  instrument  previously 
described  in  that  the  permanent  magnet  used  to  magnetize  the  armature, 
or  rather  the  "armatures"  in  this  case,  is  situated  under  the  base  of  the 
instrument. 


FIG.  226. — Type   of  polar  relay  used  by  the  Postal  Telegraph- Cable  Company.     The 
permanent  magnet  is  mounted  under  the  base. 

Among  the  other  types  of  polar  refay  in  use  might  be  mentioned  the 
"Krum"  relay,  which  instead  of  employing  permanent  magnets  to  hold  the 
armature  in  connection  with  the  open  or  the  closed  contact  of  the  local 
sounder  circuit,  has  an  extra  pair  of  magnets,  one  beside  the  main-line  and 
one  beside  the  artificial-line  magnets,  which  are  constantly  charged  from 
a  separate  source  of  current,  serving  the  same  purpose  as  the  permanent 
magnet  used  in  other  types  of  relay. 

Another  efficient  type  of  instrument  is  that  known  as  the  Wheatstone 
polar  relay,  in  which  the  pivot  of  the  vertical  armature  rests  on  one  end, 
thus  effecting  a  considerable  reduction  in  the  mechanical  inertia  of  the  moving 
element.  Also,  the  magnet  coils  are  somewhat  longer  than  in  the  ordinary 
types  of  relay.  The  windings  have  a  comparatively  high  resistance,  but  as 
they  are  connected  in  multiple  for  high-speed  work,  the  total  resistance  is 
reduced  to  one-fourth,  and  the  time-constant  of  the  relay,  as  an  indirect 
result  is  also  reduced.  In  this  type  of  relay  there  are  two  armatures, 
both  mounted  on  a  common  shaft,  and  so  situated  that  their  lower  ends  are 
under  the  influence  of  a  permanent  magnet.  Each  relay  is  equipped  with 


DUPLEX  TELEGRAPHY 


261 


FIG.  227.— Binding-post  and  internal  connections  of  artificial  line  rheostat— Postal  type. 


262  AMERICAN  TELEGRAPH  PRACTICE 

four  magnets,  and  when  current  traverses  the  windings;  two  poles  repel  and 
two  poles  attract  the  armature. 

The  artificial  line  rheostat,  and  the  artificial  capacity  used  in  connection 
with  polar  duplex  apparatus  to  "balance"  the  resistance  and  capacity  of 
the  actual  line  are  illustrated  theoretically  in  Fig.  219. 

Figure  227  shows  the  actual  internal  and  external  connections  of  the  rheo- 
stat and  the  condensers  which  make  up  the  artificial  line.  The  particular  type 
of  rheostat  illustrated  is  that  used  by  the  Postal  Telegraph-Cable  Company. 
It  will  be  seen  that  the  artificial  line  side  of  the  polar  relay  is  connected  to 
the  binding-post  L  of  the  rheostat,  from  which  point  there  is  a  circuit  to 
ground,  via  the  resistance  coils,  marked  "tens,"  "hundreds,"  and  "thou- 
sands, "  by  means  of  which  the  total  resistance  of  the  artificial  line  may  be 
varied  from  zero  to  11,100  ohms  in  order  to  balance  the  resistance  of  any 
line  wire  which  may  be  connected  into  the  set.  It  will  be  noticed  also,  that 
from  the  binding-post  L  there  are  two  condenser  circuits  to  ground,  the 
first  and  second  condensers  being  in  series  with  variable  timing  resistances. 
The  first  and  second  group  of  resistance  coils  are  connected  with  binding- 
posts  C1  and  C2  respectively,  via  rheostat  arms  which  may  be  moved  from 
one  contact  button  to  another;  so  to  insert  any  desired  value  of  timing 
resistance  in  series  with  the  condensers. 

Each  of  the  condensers  has  a  capacity  of  3  microfarads,  and  as  they  are 
connected  in  parallel,  there  is  available  a  total  capacity  of  6  microfarads 
with  which  to  balance  the  static  charge  and  discharge  effects  of  the  actual 
line.  The  capacity  of  the  condensers  being  variable,  any  desired  capacity 
may  be  obtained  simply  by  turning  a  knob  mounted  on  the  top  of  each 
condenser.  The  "ground"  switch  shown  to  the  right  of  the  transmitter,  or 
pole-changer,  when  thrown  to  the  right,  places  the  home  battery  to  line. 
For  the  sake  of  clearness  the  main-line  battery  connections  are  omitted 
from  Fig.  227,  but  it  is  understood  that  when  the  armature  tongue  of  the 
transmitter  is  in  the  closed  position  as  shown,  main-line  battery  of  one 
polarity  is  connected  to  line,  and  when  the  tongue  is  in  contact  with  the 
back-stop,  battery  of  the  opposite  polarity  is  connected  with  the  line  by 
way  of  the  ground  switch  and  the  polar  relay. 

When  the  ground  switch  is  thrown  to  the  left,  it  is  evident  that  the  home 
battery  is  disconnected  from  the  line,  and  that  the  incoming  signals  after 
passing  through  the  relay  have  a  path  to  ground  via  a  600  ohm  resistance 
coil' contained  within  the  rheostat  box.  The  location  of  this  ground-coil 
should  be  kept  in  mind,  as,  presently  we  shall  again  refer  to  it  in  connection 
with  "balancing." 

OPERATION  OF  THE  POLAR  DUPLEX 

Figure  228  shows  the  connections  of  the  main-line  and  local  circuits  of 
the  polar  duplex. 


DUPLEX  TELEGRAPHY 


263 


Complete  equipment  at  both  ends  of  a  duplexed  circuit  are  shown  so 
that  the  various  operations  may  be  treated  with  regard  to  their  effects 
upon  the  apparatus  at  both  ends  of  the  line. 

PC  and  PC'  are  the  pole-changers  at  stations  A  and  B  respectively 
while  PR  and  PR'  are  the  polar  relays,  K  and  Kr  the  signaling  keys,  locally 
controlling  the  movements  of  the  pole-changer  armature  in  each  case. 

The  dynamos  which  furnish  current  for  the  operation  of  the  main-line 
relays,  are  shown,  two  at  each  end.  In  each  case  one  of  the  dynamos  has 
its  positive  terminal  connected  with  the  back-stop  of  the  pole-changer,  while 


FIG.  228. 

the  other  dynamo  has  its  negative  terminal  connected  with  the  closed-con- 
tact of  the  pole-changer. 

The  resistance  coils  and  condensers  which  comprise  the  artificial  line, 
are,  at  each  end  of  the  main-line  circuit;  marked  AL. 

In  Fig.  228  the  pole-changers  at  each  end  of  the  line  are  closed,  that  is, 
the  armature  levers  of  the  pole-changers  in  each  case  are  in  contact  with 
their  front-stops,  due  to  the  fact  that  the  signaling  keys  K  and  K'  are  closed, 
This  places  to  line  at  each  end  a  200  volt  negative  battery.  As  the  batteries 
are  of  equal  potential,  no  current  will  flow  over  the  main  line.  At  the 
instant  both  pole-changer  armatures  make  contact  with  their  back-stops — 
thus  placing  opposing  battery  to  line — the  levers  of  the  polar  relays  at  each 
end  are  moved  into  contact  with  their  back-stops,  thereby  opening  the 
local  reading  sounder  circuits  at  each  end. 

At  this  point  it  is  important  to  gain  a  correct  understanding  of  why  the 
armatures  of  the  polar  relays  at  each  terminal  station  are  attracted  toward 
either  contact  when  the  main-line  batteries  at  each  end  of  the  line  are  in 
opposition.  The  explanation  is  that  when  the  terminals  of  a  wire  are  at 


264  AMERICAN  TELEGRAPH  PRACTICE 

equal  potentials,  no  current  will  flow  in  the  wire.  Therefore,  when  like 
poles  of  identical  potential  are  to  line,  as  in  the  case  before  us,  it  is  apparent 
that  the  terminals  of  the  main-line  wire  are  at  equal  potential.  An  entirely 
different  condition,  however,  exists  with  regard  to  the  artificial  line  at  each 
end.  As,  in  each  case,  one  end  of  the  artificial  line  is  connected  with  the 
earth  (which  is  at  zero  potential),  there  is  presented  to  the  outgoing  currents 
from  each  station  a  path  to  ground  via  the  artificial  line  magnet  of  the 
polar  relay.  On  each  occasion,  therefore,  when  like  poles  are  to  line  at 
each  end,  current  from  the  home  battery  flows  through  the  artificial  line 
and  the  armature  of  the  polar  relay  is  attracted  toward  its  back-stop  if  the 
opposing  batteries  are  positive  and  toward  its  front  stop  if  the  opposing 
batteries  are  negative. 

In  order  to  carry  on  transmission  in  both  directions  at  the  same  time  it  is 
necessary  that  the  operator  at  A  shall  be  able  to  control  the  movements  of 
the  armature  of  the  relay  at  B  regardless  of  which  pole  of  his  battery  B  has 
to  line.  Also  that  the  operator  at  B  shall  be  able  to  control  the  movements  of 
the  relay  armature  at  A  regardless  of  which  pole  of  his  battery  A  has  to  line. 

Suppose  the  operator  at  B  should  depress  his  key  (while  the  key  at  A 
is  open),  thereby  placing  the  tongue  of  his  pole-changer  in  contact  with 
the  negative  pole  of  the  main-ine  battery  at  B,  the  result  will  be  that  the 
main-line  coil  of  the  relay  at  A  will  be  energized  and  its  tongue  attracted 
toward  its  closed-contact,  thereby  operating  sounder  S. 

It  is  evident,  of  course,  that  current  continues  to  flow  through  the  artifi- 
cial line  coil  of  the  relay  at  A,  but  owing  to  the  fact  that  the  current  strength 
in  the  main-line  coil  of  the  relay  is  twice  that  in  the  former,  and  in  the  opposite 
direction,  it  is  plain  that  the  magnetism  in  the  core  of  the  relay  at  A  is 
reversed,  and  the  armature,  as  a  result  thereof,  moves  into  contact  with  its 
front-stop.  If  what  has  previously  been  stated  is  true,  the  armature  of  the 
relay  at  B  should  have  remained  passive  to  the  reversal  of  current  sent  out 
from  B  when  the  key  at  B  was  closed.  That  this  is  so  is  apparent,  for, 
although  the  magnetism  in  the  artificial  line  magnet  of  the  relay  at  B  has  now 
been  neutralized  due  to  the  presence  of  current  in  the  main-line  coil  of  the 
relay,  the  armature  is  held  in  the  open  position  by  the  action  of  the  permanent 
magnet  associated  therewith.  In  other  words,  nothing  has  happened  so  far 
to  cause  the  armature  of  the  main-line  relay  at  B  to  change  its  position, 
therefore,  it  remains  in  the  position  taken  when  last  it  was  caused  to  move  by 
a  surplus  of  magnetism  in  one  coil  over  that  obtaining  in  the  other  magnet 
coil.  Similarly,  when  A  alone  closes  his  signaling  key,  the  relay  at  B  responds, 
while  the  relay  at  A  does  not.  When  the  signaling  keys  at  both  ends  are 
depressed,  the  line  currents  once  more  are  in  opposition,  and,  as  in  this  case 
the  currents  flowing  through  the  artificial  lines  at  each  end  are  in  the  reverse 
direction  of  that  taken  when  both  keys  were  open,  the  relay  armatures  at  each 
end  are  caused  to  move  into  contact  with  their  front-stops. 


DUPLEX  TELEGRAPHY 


265 


In  effect,  therefore,  when  the  operator  at  A  attempts  to  register  a  "dot" 
on  the  relay  at  B,  at  the  same  instant  that  the  operator  at  B  intends  to 
register  a  "dot"  on  the  relay  at  A,  each  station  causes  to  be  produced  in  his 
own  relay  the  signal  intended  to  be  transmitted  from  the  distant  end  of  the 
line.  Or,  the  foregoing  might  be  paraphrased  thus:  the  relay  at  A  will  be 
closed  whenever  the  key  at  B  is  depressed,  regardless  of  whether  A  is  sending 
or  idle;  and  the  relay  at  B  will  close  whenever  the  key  at  A  is  closed  whether 
B  is  sending  or  idle,  but  in  neither  case  will  the  signals  transmitted  from 
either  end  conflict  with  those  originating  at  the  distant  station. 


SEVERAL  DUPLEX  SETS  WORKED  FROM  ONE  PAIR  OF  DYNAMOS 

In  the  duplex  circuit  diagrams  heretofore  given,  two  dynamos  have  been 
shown  at  each  station  as  an  integral  part  of  each  set.  It  should  be  under- 
stood, however,  that  in  practice,  two  machines,  one  delivering  a  positive 
potential  and  the  other  a  negative  potential, 
are  used  to  supply  current  for  a  number  of 
lines. 

In  Fig.  229,  two  200- volt  dynamos  of  oppo- 
site polarities  are  shown  connected  to  separate 
busbars.  Instead  of  four  wires  leading  there- 
from to  pole-changers  of  duplex  and  quad- 
ruplex  sets,  any  number  of  sets  may  be  con- 
nected thereto,  depending  upon  the  capacity 
of  the  dynamos  employed. 

The  four  wires  shown  in  Fig.  229  leading 
from  the  positive  busbar  are  connected  to  the 
back-stops  of  four  different  pole-changers,  and 
the    four    wires    leading    from    the    negative       FIG.  229.— Several  duplex  sets 
busbar  are  connected  to  the  front-stops  of  the  worked  from  one  pair  of  dynamos, 
same   four   pole-changers.     One   pair   of  ma- 
chines, therefore,  serves  to  operate  four  or  more  duplexes. 

Each  separate  branch  is  fused,  and  has  in  series  with  the  fuse  F,  a  protec- 
tive resistance  coil  C,  or  a  lamp  which  in  any  case  may  have  a  resistance  of 
200,  300  or  600  ohms,  depending  upon  the  value  desired  in  any  circuit  that 
may  be  connected  thereto. 


-200 


"LOCAL"  CIRCUIT  CONNECTIONS 

In  the  preceding  text-matter  describing  duplex-circuit  operation,  in 
several  instances  reference  is  made  to  the  "open"  and  "closed"  contacts  of 
relays,  transmitters  and  pole-changers. 

It  might  be  here  stated  that  instead  of  employing  one  dynamo  to  operate 


266 


AMERICAN  TELEGRAPH  PRACTICE 


each  pole-changer,  each  sounder,  etc.,  one  machine  having  an  output  of  6 
volts,  24  volts,  40  volts  or  any  desired  e.m.f.  (depending  upon  the  resistance 
of  windings  of  local  instruments,  and  upon  the  current  values  desired)  may 
be  availed  of  to  feed  a  large  number  of  such  circuits. 

Figure  230  shows  four  separate  leads  from  a  40-volt  positive  busbar,  two 
of  which  are  shown  connected  to  local  circuits.  The  upper  wire  is  connected 
through  the  magnet  winding  of  a  pole-changer,  via  a  circuit  controlling  key. 
The  opposite  terminal  of  the  winding  is  connected  to  ground  through  a  current 
regulating  resistance  coil  C  which  may  have  any  desired  value.  Inasmuch 
as  the  negative  terminal  of  the  dynamo  is  permanently  grounded,  closing 
the  signaling  key  establishes  a  completed  circuit  through  the  winding  of  PC 


Relay 


C; 


FIG.  230.  —  Several  duplex  and  quadruplex  local  circuits  operated  from  a  common  source 

of  e.m.f. 

and  ground  coil  C,  thus  energizing  the  magnet  of  PC,  and  causing  the  arma- 
ture tongue  to  move  into  contact  with  the  front-stop,  or  closed  pole.  When 
the  key  is  opened  the  circuit  is  broken,  permitting  the  retractile  spring  to 
pull  the  armature  tongue  into  contact  with  the  back-stop  or  open  pole. 
The  second  wire  (Fig.  230)  leading  from  the  busbar  of  the  local  circuit 
dynamo  is  shown  connected  with  the  armature  tongue  of  a  relay.  When 
the  electromagnet  of  the  relay  is  energized  due  to  the  presence  of  current 
in  the  main  line  connected  through  it,  the  armature  is  attracted  toward  the 
closed  contact,  meaning  that  the  circuit  starting  at  the  local  dynamo  is 
extended  through  the  relay  armature,  closed-contact,  and  on  through  the 
magnet  windings  of  the  sounder  to  ground  through  the  resistance  coil  C. 


THE  BATTERY  DUPLEX 

Figure  231  shows  the  theoretic  connections  of  the  main-line  instruments 
used  to  operate  a  polar  duplex  by  means  of  gravity  battery. 

In  this  duplex  arrangement  the  pole-changer  consists  of  two  double-con- 
tact relays,  or  transmitters.  The  transmitters  are  connected  in  series,  that 
is,  one  signaling  key  controls  the  operation  of  both  instruments,  so  that  both 


DUPLEX  TELEGRAPHY 


267 


armatures  are  in  the  closed  position  at  the  same  time,  and  in  the  open  position 
at  the  same  time;  depending  upon  whether  the  key  is  open  or  closed. 

It  will  be  seen  at  a  glance,  that  when  both  armature  levers  are  in  contact 
with  their  back-stops  the  positive  pole  of  the  row  of  gravity  cells  is  connected 


Line 


Battery 

I-H-H-H-H-! 


FIG.  231. — Theory  of  the  gravity  battery  duplex. 

to  line  via  the  tongue  of  transmitter  No.  i,  and  at  the  same  time  the  negative 
pole  of  the  battery  is  "grounded"  via  the  tongue  of  transmitter  No.  2. 
Conversely,  when  the  signaling  key  is  closed  and  both  tongues  are  against 
their  front-stops,  the  negative  pole  of  the  battery  is  connected  to  line,  and  the 
positive  terminal  of  the  battery  to  ground.  The  operation  of  the  key;  con- 


FIG.  232. — Actual  connections  gravity  battery  duplex. 

trolling  as  it  does  simultaneously  the  operation  of  both  transmitters,  results 
in  alternate  positive  and  negative  impulses  being  sent  to  line,  the  same  as 
when  two  dynamos  of  opposite  polarities  are  used. 

In  other  respects  the  connections  are  the  same  as  in  the  dynamo  polar 
duplex. 

Figure  232  shows  the  actual  circuit  connections  of  the  battery  duplex. 

THE  "  BRIDGE"  DUPLEX 

The  single-current  duplex,  and  the  polar  duplex,  being  based  on  the  differ- 
ential principle  are  dependent  upon  producing  an  equality  of  current  strengths, 


268 


AMERICAN  TELEGRAPH  PRACTICE 


while  the  bridge  duplex  which  is  based  upon  the  well-known  Wheatstone 
bridge  principle  is  dependent  upon  producing  an  equality  of  potentials. 

Figure  233  shows  two  stations  A  and  B  at  either  end  of  a  line  wire  equip- 
ped with  bridge  duplex  apparatus. 

B  and  Bf  are  the  main-line  batteries  at  A  and  B  respectively.  AL  in 
each  case  represents  the  artificial  line  at  either  end.  R  and  Rf  are  two 
artificial  resistances  of  equal  value,  likewise  r  and  r'  at  station  B.  At  each 
end  of  the  line  the  relays  are  connected  between  the  points  c  and  d  of  the 
"bridge"  formed  by  the  line  wire  and  the  artificial  line  resistance.  Closing 
the  key  at  A  sends  out  a  current  which  divides  at  a,  half  passing  over  the  line 
wire  to  station  B  and  reaching  earth  via  the  apparatus  at  that  end  of  the  line, 
while  the  other  half  passes  through  the  artificial  line  at  A ,  reaching  the  earth 


Line 


Ti 


FIG.  233. — Theory  of  the  bridge  duplex. 


at  that  end  of  the  circuit.  Inasmuch  as  the  points  c  and  d  are  equidistant, 
ohmically,  from  the  point  #,  their  potential  values  are  identical,  and  no  current 
will  flow  through  the  windings  of  the  relay  at  A.  This  is  true,  of  course, 
only  when  the  resistance  of  the  artificial  line  at  A  is  made  equal  to  the  re- 
sistance of  the  actual  line  to  ground  at  the  distant  end.  The  relay  at  A, 
therefore,  is  not  affected  when  A  sends  to  B.  The  same  condition  prevails 
when  B  alone  sends  to  A .  Signals  from  A  operate  the  relay  at  B  because  the 
incoming  signals  have  a  joint  path  made  up  of  the  branches  c-d  and  c-a, 
thus  setting  up  a  difference  of  potential  between  the  points  c  and  d  sufficient 
to  operate  the  relay. 

The  operations  which  take  place  with  different  key  combinations  at 
either  end  of  the  bridge  duplex  may  be  traced  without  difficulty. 

Since  the  line  relay  employed  in  the  bridge  duplex  does  not  need  to  be 
differentially  wound,  it  is  evident  that  any  ordinary  relay  may  be  used  with 
this  method  of  duplexing.  It  is  apparent,  also,  that  the  outgoing  currents 
do  not  pass  through  the  windings  of  the  home  relay,  and,  as  the  currents 
pass  directly  to  line,  there  is  a  minimum  amount  of  retardation  in  the  send- 
ing circuit.  And,  further,  it  is  claimed  for  the  bridge  duplex  that  its  line 
relays,  on  account  of  their  position  in  the  bridge,  are  not  as  responsive  to 
induced  line  disturbances  or  to  earth  currents  as  are  the  line  relays  in  the 


DUPLEX  TELEGRAPHY 


269 


differential  duplex.  This  is  due  to  the  fact  that  in  the  bridge  system  only 
a  portion  of  the  line  currents  pass  through  the  relay,  no  matter  whether 
the  currents  are  the  result  of  an  impressed  e.m.f.,  of  induction,  or  of  con- 
duction from  neighboring  circuits,  while  in  the  differential  duplex  all  currents 
existing  in  the  main  line  pass  through  the  windings  of  the  line  coil  of  the 
relay. 

The  bridge  duplex  has  been  more  highly  developed  in  Europe  than  in 
America,  and  several  of  the  refinements  applied  to  its  operation  there  are 
particularly  noteworthy  as  having  a  bearing  on  the  general  subject  of  high- 
speed signaling. 

These  refinements  include  the  application  of  the  signaling  condenser 
and  the  reading  condenser,  Fig.  234. 


sc 


Line 


5C 


FIG.  234. — Signaling  condensers  and  reading  condenser  applied  to. the  bridge  duplex. 


SIGNALING  CONDENSERS 

As  has  previously  been  stated,  the  electrostatic  capacity  of  the  line  wire 
must  be  satisfied  in  any  given  case  before  final-current  values  obtain  in  the 
circuit.  Although  the  time  required  for  the  current  to  reach  its  maximum 
value  is  independent  of  the  value  of  the  e.m.f.  employed,  the  time  required 
for  the  current  to  reach  a  certain  percentage  of  its  final  value  is  directly 
dependent  upon  the  value  of  the  potential  applied  to  the  circuit. 

It  is  well  known  that  when  a  terminal  potential  of,  say,  250  volts  is  ap- 
plied to  a  line  the  required  operating  current  strength  will  actuate  the  relay 
at  the  remote  end  of  the  line  in  approximately  half  the  time  required  to 
produce  the  same  effect  with  an  applied  e.m.f.  of  125  volts.  Calculations 
of  this  kind,  of  course,  require  that  the  current  resulting  from  the  lower 
value  of  e.m.f.  will  have  sufficient  strength  to  operate  the  relays  satisfac- 
torily. If,  now,  we  consider  the  circuit  conditions  prevailing  when  the  signal- 
ing condensers  SC  (Fig.  234)  are  connected  in  shunt  with  the  bridge  resist- 
ance, it  may  be  seen  that  the  presence  of  these  condensers,  in  effect,  create 


270  AMERICAN  TELEGRAPH  PRACTICE 

a  momentary  short  circuit  around  the  3,ooo-ohm  bridge  resistances.  This 
interval,  although  brief,  is  sufficient  to  permit  of  the  application  of  maximum 
battery  potential  to  the  line,  which  results  in  an  initial  current  value  at  the 
distant  end  of  the  line,  equal  to  that  which  would  obtain  if  the  3,ooo-ohm 
resistance  were  not  a  part  of  the  circuit.  After  the  condenser  and  the  line 
have  become  charged  by  the  initial  impulse,  the  final-current  strength  builds 
up  through  the  circuit  which  includes  the  3,ooo-ohm  resistance  as  a  portion 
thereof.  The  ultimate  value  of  the  current  in  the  circuit  will,  therefore,  be 

less  than  that  at  first  prevailing  at  the  receiving  end.     Obviously  the  final 

£ 
current  strength  will  have  an  ^  value. 

Inasmuch  as  the  3,ooo-ohm  bridge  coil  on  the  artificial  line  side  also  is 
shunted  with  a  condenser  having  a  capacity  adjusted  to  a  value  equal  to 
that  shunting  the  3,ooo-ohm  bridge  coil  in  the  line  side,  it  is  plain  that  exactly 
like  conditions  exist  in  each  branch  of  the  circuit  at  the  same  time. 

When  the  line  current  is  reversed  it  is  obvious  that  the  condensers  will 
discharge  in  a  direction  coinciding  with  that  due  to  the  alternate  battery 
pole.  Thus  the  total  value  of  the  e.m.f.  actuating  the  circuit  will  be  that 
of  the  terminal  battery  plus  that  existing  as  charge  in  the  condensers. 

On  each  occasion,  therefore,  that  the  condensers  are  taking  on  or  giving 
up  their  charge,  the  initial  portion  of  the  signaling  impulses  in  either  direc- 
tion has  a  path  other  than  that  presented  through  the  3,ooo-ohm  bridge 
coils.  It  may  be  observed  that  the  effect  of  the  condenser  discharge  is  to 
greatly  expedite  the  discharge  of  the  line  wire,  and  in  this  regard  it  is  found 
that  the  best  results  are  attained  when  the  capacity  of  the  condenser  is  made 
equal  to  that  of  the  line. 

THE  READING  CONDENSER 

The  reading  condenser,  or  " shunted"  condenser  as  it  is  sometimes  called 
(RC  Fig.  234),  in  British  Post  Office  practice  consists  of  a  group  of  three 
resistance  units  having  individual  values  of,  2,000,  4,000,  and  8,000,  ohms 
or  a  total  of  14,000  ohms,  shunted  by  an  adjustable  condenser  having  a  total 
capacity  of  7  1/2  microfarads. 

The  function  of  the  shunted  condenser  is  to  balance  the  effects  of  self- 
induction  of  the  signaling  relay. 

In  a  preceding  chapter  it  was  pointed  out  that  when  the  direction  of 
current  flowing  in  a  coil  of  wire  or  a  magnet  is  reversed  the  effect  of  self- 
induction  between  the  turns  of  wire  in  the  magnet  is,  in  the  first  place,  to 
retard  the  rise  of  current  strength  in  the  circuit  of  which  the  winding  forms 
a  part  and  when  on  each  occasion  the  circuit  is  opened  the  effect  of  self- 
induction  is  to  delay  the  fall  to  zero  current. 

The  presence  of  the  shunted  reading  condenser  provides  that  the  com- 


DUPLEX  TELEGRAPHY 


271 


mencement  of  the  reversal  of  magnetism  in  the  cores  of  the  relay  will  take 
place  at  the  instant  the  transmitter  tongue  at  the  distant  end  of  the  line 
leaves  either  the  positive  or  the  negative  battery  contact,  so  that  the  process 
of  reversing  has  progressed  to  a  certain  extent  by  the  time  the  tongue  of  the 
distant  transmitter  reaches  the  opposite  battery  contact,  or  the  (''ground") 
contact,  as  the  case  may  be,  and  an  effect  is  produced  which  balances  the 
effects  of  self-induction  by  hastening  the  rise  and  fall  of  the  operating  cur- 
rent in  the  circuit  at  the  instant  desired. 

The  amount  of  capacity  and  resistance  which  yields  the  best  result  in 
a  given  case,  naturally  is  dependent  upon  the  particular  properties  of  the  line 
conductor  under  consideration,  and  can  be  determined  only  under  working 
tests. 


THE  WESTERN  UNION  BRIDGE  DUPLEX 

Figure  2340  shows  the  theory  of  the  bridge  duplex  recently  adopted  by 
the  Western  Union  Company.     In  this  duplex  the  bridge  arms  consist  of 


Line 


FIG.  2340. — Western  Union  bridge  duplex. 

the  companion  windings  of  an  impedance  coil  (5  U)  each  arm  having  an  ohmic 
resistance  of  500  ohms  (see  the  impedance  coil,  Fig.  279). 

In  Fig.  2340,  the  main-line  circuits  at  each  end  of  a  duplexed  line  are 
shown,  in  which  D  represents  the  main-line  dynamos,  L,  resistance  lamps, 
MA,  milammeters,  PR,  polar  relays,  PC,  pole-changers,  r,  retardation 
resistances,  5^7,  impedance  coils,  SC,  spark  condensers,  MR,  main-line 
adjustable  resistances,  CR,  compensating-circuit  adjustable  resistance,  AL, 
regular  artificial-line  adjustable  resistances,  C,  static  compensating  con- 
densers. 

The  operation  of  this  duplex  will  be  better  undertsood  after  the  reader 
has  gone  through  the  matter  describing,  the  Western  Union  quadruplex 
(Fig.  276). 


272  AMERICAN  TELEGRAPH  PRACTICE 

THE  HIGH-POTENTIAL  "LEAK"  DUPLEX 

In  those  telegraph  installations  where  the  only  dynamos  in  service  are 
those  required  to  operate  the  long  quadruplexes,  the  "leak"  method  of  re- 
ducing high  potentials  to  values  sufficient  to  operate  circuits  duplex,  is 
sometimes  employed. 

This  method  is  due  to  Mr.  Minor  M.  Davis  and  was  introduced  on  the 
lines  of  the  Postal  Telegraph-Cable  Company  several  years  ago. 

Figure  235  shows  the  theoretic  arrangement  of  circuits  of  the  leak  duplex. 

An  artificial  circuit  to  ground  is  built  up  of  coils  having  resistances  of 
800  plus  2,200  ohms,  or  a  total  of  3,000  ohms. 

Where  the  machines  available  for  quadruplex  working  have  potentials 
of  380  volts,  positive  and  negative,  respectively,  it  is  apparent  that  with 

_800 

1600 

Line 


Condenser 


FIG.  235. — Theory  of  the  high-potential  "leak"  duplex. 

an  internal  resistance  of  600  ohms  in  series  with  the  leak  resistance,  the 
nearest  ground  is  3,600  ohms  distant  from  the  battery,  at  least  that  would 
be  the  case  when  the  tongue  of  the  pole-changer  is  midway  between  its  back- 
stop and  front-stop. 

As  the  pole-changer  is  operated  its  tongue  is  caused  to  make  contact 

with  the  leak  circuit  at  a  point  either          -  of  the  total  ohmic  distance  to 

3600 

ground,  or  in  case  the  8oo-ohm  resistance  is  short  circuited  at  a  point     , 

of  the  total  ohmic  distance  to  ground.  Thus  the  available  voltage  at  the 
pole-changer  contacts  is  reduced  to  a  value  considerably  below  that  available 
at  the  brushes  of  the  machines.  The  exact  value  in  either  case  may  be 
calculated  by  means  of  either  of  the  methods  described  in  a  preceding  chap- 
ter for  determining  the  difference  of  potential  at  any  point  along  a  conductor 
possessing  resistance — between  that  point  and  ground. 

A  leak  path  to  ground  is  provided  for  each  of  the  high-voltage  gen- 
erators, so  that  the  reduction  of  voltage  may  be  made  equal  in  the  case  of 
both  positive  and  negative  machines. 

The  possible  connections  are  such  that  three  different  potential  values 
may  be  availed  of  as  desired. 

When  the  circuit-controlling  plugs  are  removed  from  the  2,2oo-ohm 


DUPLEX  TELEGRAPHY 


273 


coils,  and  the  8oo-ohm  coil  in  each  circuit  is  short  circuited,  the  full  quadru- 
plex  battery  is  available.  With  the  2,2oo-ohm  coils  in  circuit  while  the 
8oo-ohm  coils  are  short  circuited,  the  next  lower  potential  is  available,  and 
when  the  2,2oo-ohm  coils  are  in  circuit  and  the  shunt  circuit  removed  from 
around  the  8oo-ohm  coils,  a  third  potential  value  is  available. 

Figure  236  shows  the  actual  binding-post  connections  of  the  main-line 
wiring  of  a  high-potential  leak  duplex. 


FIG.  236. — Actual  connections  of  the  high-potential  leak  duplex. 


HIGH  EFFICIENCY  DUPLEXES 

Within  recent  years  a  demand  has  been  created  for  the  development  of 
a  high  efficiency  duplex.  Among  the  causes  which  have  brought  about 
this  demand,  the  more  important  are:  the  increasing  amount  of  line  dis- 
turbance experienced  due  to  induction  from  other  wires  of  the  same  system 


IMF. 


\  Line 


FIG.  237. — Theory  of  the  high-efficiency  duplex  employed  by  the  Postal  Telegraph 

^Company. 

and  from  neighboring  conductors  carrying  high  potentials,  decrease  in  the 
efficiency  of  transmission  attributable  to  the  employment  of  semi-automatic 
transmitters  which  are  not  as  regular  in  action  as  simple  hand  transmission 
by  means  of  the  Morse  key.  Also,  the  call  for  fast  and  dependable  leased 

18 


274  AMERICAN  TELEGRAPH  PRACTICE 

wire  service  and  for  high-speed  automatic  and  printer  circuits  has  resulted 
in  a  systematic  critical  investigation  of  the  duplex  at  the  hands  of  several 
well-known  experts.  Fig.  237  shows  the  circuits  of  an  improved  differential 
duplex  recently  brought  out  by  Messrs.  Davis  and  Eaves.  The  principles 
of  operation  are  the  same  as  in  the  ordinary  differential  polar  duplex  previ- 
ously described,  but  several  capacity  and  resistance  units  have  been  com- 
bined and  applied  in  -such  relation  to  the  regular  duplex  circuits  that  not 
only  do  they  serve  to  correct  the  inherent  weaknesses  of  the  duplex,  but  to 
bring  about  action  in  certain  places  and  at  certain  intervals  which 
materially  increases  the  operating  efncieny  of  a  duplex  to  which  these 
adjuncts  are  applied.  , 

By  referring  to  Fig.  237  it  will  be  seen  that  two  5oo-ohm  non-inductive 
coils  have  been  introduced  at  the  " split"  behind  the  relay,  so  that  the  out- 
going current  has  a  joint  path,  on  the  one  hand  through  a  5oo-ohm  coil  and 
the  main-line  winding  of  the  relay,  and  on  the  other  through  the  companion 
5oo-ohm  coil  and  the  artificial-line  winding  of  the  relay.  The  presence  of 
these  coils  introduces  only  the  property  of  resistance  into  the  circuit,  as  owing 
to  the  fact  that  they  are  non-inductively  wound  there  is  no  retardation 
introduced.  The  insertion  of  the  resistance  back  of  the  relay  steadies  the 
balance  somewhat,  due  to  the  fact  that  a  considerable  proportion  of  the 
total  resistance  of  the  circuit  is  inserted  between  the  coils  of  the  relay  and  the 
ground  connection  via  either  dynamo.  The  presence  of  the  two  5oo-ohm 
coils  causes  the  condenser  connected  in  shunt  therewith  to  take  on  a  charge 
due  to  the  difference  of  potential  which  exists  between  the  points  a  and  b 
when  the  pole-changer  at  the  distant  end  of  the  line  is  operated. 

The  function  of  this  condenser  is  to  hasten  the  "turn-over"  of  magne- 
tism in  the  cores  of  the  home  relay  when  the  distant  station  sends  out 
current  reversals.  The  condenser  anticipates,  as  it  were,  the  action  which 
will  result  in  the  home  relay  when  the  tongue  of  the  pole-changer  at  the 
distant  station  reaches  the  negative  or  positive  battery  contact,  as  the  case 
may  be. 

With  the  ordinary  arrangement  of  duplex  circuits,  the  armature  lever  of 
the  home  polar  relay  remains  in  contact  with  the  closed  contact  of  its  sounder 
circuit  as  long  as  the  tongue  of  the  pole-changer  at  the  distant  station  is  in 
contact  with  its  front-stop  and  until  the  pole-changer  tongue  again  touches 
its  back-stop. 

The  action  of  the  condenser  here  considered  is  to  cause  reversal  of  magnet- 
ism in  the  relay  at  the  instant  the  tongue  of  the  pole-changer  at  the  distant 
station  departs  from  either  its  front-  or  b'ack-stop.  It  is  apparent  that  the 
charge  which  the  condenser  has  accumulated  while  the  tongue  of  the  distant 
pole-changer  has  been  in  contact  with  either  battery  pole  will  discharge 
through  the  windings  of  the  home  relay  in  a  direction  coinciding  with  that 
taken  by  the  current  resulting  from  the  next  succeeding  battery  contact  at 


DUPLEX  TELEGRAPHY 


275 


the  distant  end.  Thus,  the  current  arriving  from  the  distant  station  com- 
pletes the  work  already  begun  by  the  condenser. 

The  two  6oo-ohm  non-inductive  coils  connected  around  the  relays, 
in  series  with  one-half  microfarad  condensers,  present  to  in-coming  inductive 
disturbances  a  path  to  ground  which  does  not  lead  through  the  windings  of 
the  relay,  thus  in  large  measure  making  the  relay  immune  to  induced  currents, 
especially  from  alternating-current  sources,  and  also  to  electrostatic  and 
electromagnetic  induction  from  neighboring  wires  of  the  same  system. 

Another  benefit  derived  from  the  6oo-ohm,  i-m.f.  shunt  circuit  is  that  the 
discharge  due  to  self-inductance  of  the  relay  magnets  takes  place  through  the 
loop  circuit  thus  formed  around  the  relay  coils,  preventing  its  interference 
with  line  currents. 


ZYNAMff 

ZUFLEX 

HA/N  CIRCUITS 


FIG.  238.  —  Main  line  connections  of  the  Postal  Company's  duplex. 


Another  decided  advantage  resulting  from  the  employment  of  the  latter 
circuit  is  that  the  first  part  of  each  out-going  current  wave  gets  to  line  and 
to  the  distant  station  earlier  than  it  would  if  required  to  travel  through  the 
inductive  winding  of  the  home  polar  relay.  The  desired  movement  of  the 
armature  of  the  distant  polar  relay,  therefore,  is  well  under  way  by  the  time 
the  Ohm's  law  current  arrives. 

Other  important  features  have  been  introduced  in  connection  with  this 
high  efficiency  duplex,  among  which  might  be  mentioned  the  use  of  an 
improved  "spark-killer"  arrangement  to  control  the  sparking  which  occurs 
at  pole-changer  points  as  contact  is  alternately  made  betweeen  the  tongue 
and  the  positive  or  negative  potentials. 

Also,  a  reduced  internal-resistance  value  is  inserted  between  the  dynamo 


276  AMERICAN  TELEGRAPH  PRACTICE 

and  the  pole-changer  line  contacts,  and  an  improved  form  of  polar  relay  is 
used. 

These  features  are  referred  to  in  detail  further  along. 

Figure  238  shows  the  instrument  main-line  connections  of  the  high 
efficiency  duplex  just  described. 

CITY  LINE  DUPLEX 

Figure  239  shows  the  theoretical  connections  of  a  short-line  duplex, 
which  may  be  operated  over  a  single  wire  with  main  battery  of  one  polarity, 
at  one  end  of  the  line 

The  line  relay  at  the  main  office  is  an  ordinary  differential  non-polarized 
instrument,  the  same  as  that  used  in  connection  with  the  ordinary  single- 
current  duplex,  or  on  the  second  side  of  a  quadruplex.  At  the  branch  office 

Main  Office  Branch  Office 

Leak 

fUJWl  r>^K~n ^^ 

B    ~^ 

TR. 
. ,  A  -  High  Res.  Magnet 

FIG.  239. — City  line  duplex. 

a  special  non-polarized  differential  relay  is  employed,  the  artificial-line  coil 
of  which  has  a  winding  of  higher  resistance  than  that  of  the  main-line  coil. 

A  glance  at  the  circuit  arrangements  will  show  that  battery  is  to  line  at 
all  times,  full  potential  when  the  main-office  transmitter  is  closed,  and  a 
reduced  potential  when  the  main-office  transmitter  armature  is  in  contact 
with  its  back-stop:  the  value  of  the  reduced  potential  depending  upon  the 
resistance  value  of  the  leak  circuit  which  forms  one  path  of  a  joint  circuit  to 
ground,  the  other  path  consisting  of  the  main  line  and  the  apparatus 
at  the  branch  office,  and  the  path  to  ground  via  the  artificial  line  at  the 
main  office. 

When  the  armature  lever  of  the  relay  at  the  branch  office  is  resting 
against  its  back-stop,  the  only  path  presented  to  the  incoming  signals  is 
through  the  coils  of  the  relay  to  ground  via  the  artificial  line  at  the  branch 
office.  When  the  main  office  only  is  sending,  it  is  evident  that  inasmuch  as 
the  out-going  currents  pass  through  the  relay  at  the  main  office  differentially, 
the  armature  of  that  relay  is  not  affected,  while  the  relay  at  the  branch  office 
responds  each  time  the  armature  tongue  of  the  main-office  transmitter  closes, 
and  opens  each  time  the  tongue  of  the  main-office  transmitter  is  withdrawn 
into  contact  with  its  back-stop,  because  then  the  current  which  is  sent  to 
line  is  not  of  sufficient  strength  to  operate  the  branch-office  relay.  Ob- 
viously, the  tension  given  the  retractile  spring  attached  to  the  armature  of 


'DUPLEX  TELEGRAPHY 


277 


the  branch-office  relay  must  be  such  that  the  magnetism  produced  by  the 
reduced  current  volume  will  not  be  strong  enough  to  attract  the  armature. 

With  the  armature  tongue  of  the  branch-office  transmitter  in  the  closed 
position,  and  at  rest,  the  incoming  signals  have  a  joint-path  to  ground  at  the 


orr/cc 

TO  mOH 
SW/TCHES     TO  LCfT  -  Z  SlftlfS£T5. 


FIG.   240. — Main  office  connections  city  line  duplex. 

branch  office,  but  still  the  armature  of  the  relay  at  the  branch  office  will  re- 
spond each  time  the  main-office  transmitter  is  closed,  and  release  each  time 
the  latter  is  opened,  for  although  a  greater  current  volume  exists  in  the  main 
line  because  of  the  shorter  path  to  ground  presented,  the  total  amount  of 


ro  RIGHT     DUPLEX 

SWITCHES     TO   LEFT        Z  S/M6LE  S£TS. 


FIG.   241. — Branch  office  connections  city  line  duplex. 

magnetic  pull  on  the  armature  of  the  branch-office  relay  is  no  greater  than 
before  owing  to  the  fact  that  the  high  resistance  (and  the  most  effective)  coil 
of  the  relay  is  practically  short-circuited  by  the  newly  presented  path  to 
ground  via  the  tongue  of  the  transmitter. 


278   • 


AMERICAN  TELEGRAPH  PRACTICE 


It  is  apparent,  however,  that  when  the  armature  lever  of  the  branch- 
office  relay  is  in  contact  with  its  front-stop  the  increased  current  strength 
in  the  main-line  coil  of  the  main-office  relay  results  in  the  armature  of  that 
relay  being  attracted — the  very  result  desired,  for  it  is  when  the  tongue  of  the 
branch  office  transmitter  is  moved  into  contact  writh  its  front-stop  that  the 
armature  of  the  main-office  relay  should  be  moved  into  contact  with  its  front- 
stop. 

The  reason  why  this  type  of  duplex  is  not  suitable  for  long  lines  is  that 
the  ratio  of  operating  to  releasing  current  is  such  that  the  margin  of  current 
strength  between  these  two  values  is  not  very  great,  in  fact,  not  great  enough 
to  permit  of  fluctuation  of  current  strengths  such  as  experienced  in  the 
operation  of  long  lines. 

Figure  240  shows  the  actual  main-line  and  local  connections  of  the  city- 
line  duplex  at  the  main  office,  while  Fig.  241  shows  the  connections  at  the 
branch  office. 

At  the  main  office  a  regular  duplex  rheostat  is  used;  the  artificial-line 
circuit  being  made  up  of  the  regulation  artificial-line  coils,  and  the  "  leak  "  cir- 
cuit to  ground  being  made  up  of  the  coils  ordinarily  used  as  the  first  and  second 
condenser  circuits.  As  the  arrangement  is  intended  only  for  short  lines,  it 
is  not  necessary  to  employ  static  compensating  condensers. 


SHORT -LINE  DUPLEX,  WITH  BATTERY  AT  ONE  END  ONLY 

A  short-line  duplex  requiring  battery  at  one  end  only,  which  has  been 
employed  with  considerable  success  on  the  lines  of  the  Western  Union  Tele- 
graph Company,  is  that  known  as  the  Morris  duplex. 


Battery  Station 


FIG.  242. — Double  current  duplex  with  battery  at  one  end  only. 

The  system  was  originally  devised  by  Mr.  Gerritt  Smith,  later  improved 
by  Mr.  Morris,  and  still  more  recently  has  been  equipped  with  static  com- 
pensating accessory  apparatus  which  permits  of  its  successful  employment 
in  the  duplex  operation  of  lines  150  miles  or  more  in  length. 


DUPLEX  TELEGRAPHY  279 

Figure  242  shows  the  theoretical  main  line,  and  the  local  connections 
of  the  latest  arrangement  of  apparatus. 

The  rheostat  at  the  main,  or  battery  station,  makes  possible  the  insertion 
of  a  resistance  value  equal  to  that  of  the  line  "wire  plus  the  resistance  of  the 
rheostat  at  the  distant  office. 

The  proper  resistance  value  required  to  be  inserted  at  the  distant  office 
may  be  determined  by  measuring  the  line  current  with  the  distant  key  open, 
and  again  when  it  is  held  closed.  The  resistance  of  the  rheostat  should  be 
such  that  with  the  key  closed  the  line  current  will  be  three  times  that  obtain- 
ing in  the  circuit  when  the  key  is  open. 

The  proper  resistance  value  to  give  the  rheostat  at  the  battery  end  of  the 
line  may  be  determined  by  measuring  the  resistance  of  the  line  to  the  distant 
ground  including  the  resistance  of  the  distant  relay  and  rheostat. 

The  operation  of  this  duplex  may  easily  be  traced  by  observing  what  takes 
place  when  the  keys  are  operated,  and  when  the  transmitter  tongues  at  either 
end  are  in  the  various  possible  positions. 

SPARKING  AT  CONTACT  POINTS 

In  the  operation  of  relays  a  troublesome  spark  is  produced  as  contact  is 
made  or  broken  between  the  movable  armature  lever  and  the  stationary 
front-stop  each  time  the  local  circuit-  is  closed  or  opened.  It  is  the  effect  of 
the  extra  current  of  self-induction,  and  is  strongest  at  the  instant  the  circuit 
is  broken.  Naturally,  it  is  more  pronounced  in  wet  than  in  dry  weather, 
owing  to  the  fact  that  the  forward  and  the  backward  movement  of  the  arma- 
ture of  the  relay  is  then  more  sluggish.  The  same  is  true  in  any  state  of  the 
weather  of  relays  operating  in  lines  which  are  not  maintained  at  a  high  degree 
of  insulation.  ; 

It  has  been  found  that  the  more  rapid  the  movement  of  the  armature, 
the  less  pronounced  will  be  the  resulting  spark  at  make  and  break  of  contact. 

The  effects  observed  in  the  operation  of  telegraph  apparatus  are  in  con- 
formity with  the  general  theory  of  the  subject  as  enunciated  by  Faraday,  and 
point  to  the  conclusion  that  if  connections  and  disconnections  could  be  made 
rapidly  enough  "sparkless"  make  and  break  might  be  accomplished.  Ray- 
leigh  has  shown  that  when  a  circuit  is  broken  at  velocities  of  the  order  of  one 
meter  (39.37  in.)  per  second,  there  is  no  evidence  of  sparking  between  contact 
points. 

It  is  found  that  with  a  quick-moving  armature,  a  much  closer  adjustment 
is  possible  than  with  a  slow-moving  armature.  If  the  current  traversing 
the  magnet  windings  of  the  instrument  is  weak,  thus  necessitating  a  weak 
retractile  spring,  it  is  found  that  a  wide  adjustment  between  tongue  and 
contact  point  is  necessary  in  order  to  avoid  sparking,  but  with  a  strong 
magnetic  pull  on  the  armature,  and  a  strong  retractile  spring,  insuring  quick 


280  AMERICAN  TELEGRAPH  PRACTICE 

movement  of  the  armature  in  each  direction,  points  may  be  set  much  closer 
together  without  danger  of  excessive  sparking. 

By  far  the  greatest  amount  of  trouble  experienced  due  to  sparking  at 
contact  points  is  that  encountered  in  the  operation  of  transmitters  and 
pole-changers  used  in  duplex  and  quadruplex  telegraphy. 

In  the  case  of  a  pole-changer,  the  negative  terminal  of  a  375-volt  dynamo 
may  be  connected  to  the  armature  front-stop,  while  the  positive  terminal 
of  another  375-volt  dynamo  may  be  connected  to  the  armature  back-stop  of 
the  instrument,  and  as  the  armature  lever  (which  is  connected  to  the  main 
line  via  the  windings  of  the  line  relay)  plays  between  these  contact  points, 
there  is  an  ever  present  danger  of  arcing,  due  to  the  difference  of  potential 
(amounting  to  750  volts),  existing  between  the  front-  and  back-stops  sepa- 
rated by  the  air-gap  traversed  by  the  lever  in  its  movements  to  and  fro. 

When  an  arc  forms  between  the  opposite  contacts,  the  great  heat  devel- 
oped quickly  destroys  the  metal  points  and  renders  them  unfit  for  use. 
Pole-changers  and  hand-operated  keys  which  are  directly  connected  into 
main-line  circuits  usually  have  contact  points  constructed  wholly  of,  or 
tipped  with  platinum. 

Platinum  is  the  heaviest  and  least  expansible  of  the  metals,  is  harder 
than  iron,  very  ductile,  undergoes  no  alteration  in  air,  and  resists  the  action 
of  acids. 

Silver  also1  has  been  used  to  a  considerable  extent  in  making  contact 
points,  and  while  it  is  true  that  silver  undergoes  changes  in  air,  it  is  claimed 
that  the  oxide  of  silver  formed  on  the  exposed  surfaces  is  a  better  conductor 
of  electricity  than  the  silver  itself  and  that  the  same  necessity  does  not 
exist  for  maintaining  clean  bright  surfaces  of  contact  as  is  the  case  with  other 
metals. 

It  is  probable,  however,  that  in  cases  where  the  oxide  of  silver  film  is 
allowed  to  exceed  minute  thickness,  there  is  danger  of  the  accumulation  of 
foreign  matter  of  low  conductivity  in  association  with  the  somewhat  irregu- 
lar deposit  of  oxide.  This  means  that  where  silver  contact  points  are 
employed,  it  is  the  part  of  wisdom  to  clean  the  points  with  a  fine  steel  file, 
usually  provided  for  the  purpose,  as  is  customary  with  platinum  contacts. 

When  it  is  remembered  that  in  the  operation  of  transmitters  and  pole- 
changers,  the  duration  of  contact  between  the  armature  lever  (the  line)  and 
the  stationary  contact  points  (the  main-line  battery)  is  very  brief,  if  the 
full  voltage  of  the  dynamo  is  to  be  impressed  upon  the  line  at  each  contact, 
it  would  seem  to  be  important  that  the  abutting  contacts  should  be  free  of 
foreign  matter,  have  smooth  regular  surfaces,  and  that  the  area  of  surface 
contact  should  be  such  that  no  appreciable  resistance  will  be  introduced  at 
the  instant  connection  is  made. 

1  Quite  recently  wrought  tungsten  has  been  introduced  as  a  substitute  for  platinum  in 
the  manufacture  of  electrical  make  and  break  contacts. 


DUPLEX  TELEGRAPHY 


281 


It  is  found  in  practice  that  contact  points  having  even  regular  surfaces 
and  which  are  kept  well  polished,  do  the  work  required  of  them  more  satis- 
factorily and  cause  less  trouble  from  sparking  than  points  which  are  neglected 
in  these  respects. 

Quite  a  number  of  meritorious  arrangements  have  been  proposed,  having 
in  view  the  prevention  of,  or  the  control  of  sparking  at  contact  points, 
several  of  which  methods  are  described  in  what  follows. 

The  Postal  Telegraph-Cable  Company  has  recently  adopted  a  type  of 
pole-changer  which  is  equipped  with  a  permanent  magnet  taking  the  place  of 
the  retractile  spring  formerly  used  to  draw  the  armature  tongue  into  contact 
with  the  back-stop  when  the  magnet  coils  of  the  instrument  are  de-energized. 

With  a  spring  retractile,  when  the  local  key  circuit  is  closed  and  the  pole- 
changer  coils  energized,  the  pull  against  the  forward  movement  of  the  arma- 
ture increases  as  the  armature  moves  toward  the  front-stop,  and  in  the 
reverse  movement  of  the  armature  the  pull  is  greatest  at  the  instant  the 


•5mf. 


Line 


•5mf. 


FIG.  243. — Form  of  pole  changer 
in  which  the  forward  and  backward 
movements  of  the  armature  are 
controlled  by  electro-magnets. 


FIG.  244. — Spark-controlling  arrangement 
formerly  used  by  the  Postal  Telegraph  Company. 


local  key  circuit  is  opened,  the  strength  of  pull  decreasing  as  the  armature 
travels  toward  the  back-stop.  When  a  permanent  magnet  is  employed  for 
the  purpose,  the  retractile  pull  against  the  armature  rapidly  decreases  as  the 
armature  moves  toward  the  front-stop,  and  rapidly  increases  as  the  armature 
moves  toward  the  back-stop.  It  is  believed  that  where  the  permanent 
magnet  is  employed,  it  is  possible  to  maintain  a  retractile  pull  more  nearly 
equivalent  to  that  of  the  forward  pull  produced  by  the  electromagnets,  thus 
insuring  an  equal  speed  of  armature  travel  in  either  direction.  As  in  the 
case  of  the  spring  retractile,  it  is  necessary  that  the  permanent  magnet  be 
so  mounted  that  it  may  be  adjusted  with  respect  to  its  proximity  to  the 
armature,  so  that  ageing  of  the  permanent  magnet  may  be  compensated 
for,  and  that  the  retractile  force  exerted  may  be  made  to  equal  that  of  the 
electromagnets  under  any  given  conditions  of  current  strength. 


282 


AMERICAN  TELEGRAPH  PRACTICE 


One  decided  advantage  of  the  permanent-magnet  retractile  is  that  the 
"pull"  is  constant,  thus  preventing  any  tendency  the  armature  lever  may 
have  to  rebound  from  either  back  or  front  contact  point.  Where  the  spring 
is  used  it  is  claimed  that  the  reflex  action  progressing  while  the  coils  of  the 
spring  are  in  motion,  produces  a  rebounding  movement  of  the  lever  which 
results  in  sending  to  line  a  current  impulse  somewhat  wavy  in  form. 

The  type  of  pole-changer  illustrated  in  Fig.  243  is  so  designed  with  regard 
to  the  disposition  of  electromagnets  on  either  side  of  the  armature  that  when 
it  is  desired  to  have  the  lever  move  into  contact  with,  say  the  positive  pole 
of  the  battery,  the  electromagnetic  force  holding  the  lever  against  the  opposite 
battery  contact  is  instantly  neutralized,  thus  the  armature  is  permitted  to 
move  in  the  desired  direction  without  being  restrained  by  an  opposing  force. 


•Fie.  245. 


FIG.  2450.  FIG.  245^ 

FIGS.  245,  2450  and  245^. — Johnson  coil  spark  curbing  arrangement. 

And  conversely  when  it  is  desired  that  the  lever  shall  move  into  contact 
with  the  negative  battery  pole,  the  armature  again  moves  in  the  desired 
direction  without  being  restrained  by  an  opposing  force. l 

It  will  be  observed  that  there  are  no  springs  or  permanent  magnets 
employed  in  the  operation  of  this  instrument.  The  electromagnet  on  the 
right  has  two  equal  windings  connected  differentially,  while  the  magnet  on 
the  left  has  an  ordinary  single  winding. 

With  the  highest  speed  possible  with  any  type  of  pole-changer  where  the 
armature  must  start  from  a  position  of  rest,  contact  is  broken  at  a  relatively 
low  velocity,  and  as  a  consequence  a  considerable  amount  of  sparking  takes 
place. 

Various  combinations  of  resistance  coils  and  condensers  have  been 
employed  successfully  in  limiting  the  amount  of  spark  formed  at  contact 
points.  The  arrangement  illustrated  in  Fig.  244  was  for  a  time  used  by  the 
Postal  Telegraph- Cable  Company,  in  connection  with  pole-changers  operat- 
ing in  multiplex  circuits.  It  will  be  seen  that  while  the  armature  lever 
makes  and  breaks  contact  with  the  individual  dynamo  terminals  in  the 

1  This  is  aside  from  the  natural  opposition  to  movement,  due  to  gravity,  to  inertia,  and 
to  bearing  friction. 


DUPLEX  TELEGRAPHY 


283 


usual  manner,  a  condenser  discharge  path  is  at  all  times  maintained  around 

the  contact  points,  the  armature  being  connected  to  the  middle  of   the 

discharge  circuit  by  way  of  a  4oo-ohm  resistance  coil,  wound  non-inductively. 
The  above  arrangement  was  displaced  on  the  lines  of  the  Postal  Company 

by  a  form  of  induction  coil  known  as  the 

"Johnson"  coil,  see  Figs.  245,  2450  and 

2456. 

This    arrangement    consists   of   three 

separate  windings  of  german  silver  wire 

of  small  gage,  wound  on  a  wood  bobbin 

with  an  air  core,  the  spool  thus  formed 

being  about  7  in.  long  and  i  in.  in  diameter. 

The  coils,  although  wound  one  on  top  of 

the  other,  are  thoroughly  insulated  from 

each  other  by  a  double  cotton  covering 

saturated  with  paraffine.     As  indicated  in 

Fig.  245,  one  end  of  each  winding  is  left 

open,  while  the  opposite  ends  of  the  wind- 
ings are  connected  to  the  battery  contact 

points  and  the  armature  of  the  pole-changer 

as  depicted  in  Fig.  2456,  the  center  winding 

(provided  with  a  red  covering  to  distin- 
guish it  from  the  top  and  bottom  windings) 

being  connected  with  the  armature,  while 

the  top  and  bottom  windings  are  connected 

with    the   positive  and  negative  battery 

terminals  of  the  pole-changer. 

The  inductive  action  that  takes  place  between  the  contiguous  windings 

has  the  effect  of  absorbing  and  dissipating  the  energy  of  the  spark.     In  cases 

where  the  tendency  toward  sparking  is  exces- 
sive it  is  helpful  to  connect  two  of  these 
"coils"  in  parallel,  similarly  to  the  way  in 
which  two  condensers  are  connected  in 
parallel. 

Recently  the  Postal  Telegraph  Company 
has   adopted   the  spark-killing  arrangement 
of  shown   in    Fig.   246,  in  which  each  battery 


FIG.  246. — Present    method  of  spark 
control  used  by  the  Postal  Company. 


.25  mf. 


FIG.    247. — Present    method 

spark  control  used  by  the  Western  terminal  of  the  pde-'changer  is  provided  with 
Union  Company.  . 

a  discharge  path  to  ground  through  a  one- 
half  microfarad  condenser. 

The  arrangement  used  by  the  Western  Union  Telegraph  Company  to 
limit  sparking  at  pole-changer  contact  points  is  illustrated  in  Fig.  247,  in 
which  a  i/4-m.f.  condenser  connected  in  series  with  a  2o-ohm  lamp  of  the 


284 


AMERICAN  TELEGRAPH  PRACTICE 


incandescent  pattern  is  placed  across  the  battery   terminals  of  the  pole- 
changer. 


THE  "MAKE"  SPARK 

It  has  been  stated  that  the  spark  which  occurs  at  the  instant  contact 
is  broken,  is  due  to  the  extra  current  of  self-induction  of  the  circuit.  It 
might  here  be  stated  that  the  spark  which  occurs  between  the  armature  contact 

and  the  battery  terminal  of  a  pole-changer  at 
the  instant  contact  is  "made"  is  due  to  the 
static  discharge  from  the  main  and  artificial 
lines,  which  takes  place  during  the  brief  instant 
that  actual  contact  is  being  made. 

By  means  of  a  circuit  arranged  as  in  Fig. 
248,  the  production  of  the  "make"  and  of  the 
"break"  spark  may  be  observed,  and  the  cause 


IR 


w^         •  ',1 

Wlth  2  m  COntaCt  Wlth 


i 
als°  m 


FIG    248,-Circuit  arrange-  of  each  determined. 
ment    for    demonstrating   pro- 
duction  of  the  "make"  and  the 
"break"  sparks.  contact  with  a  produces  a  strong  spark  at  the 

instant   contact   is   made,   while  no  spark  ap- 
pears as  contact  between  a  and  i  is  broken. 

No  perceptible  sparking  takes  place  as  a  is  moved  into  contact  with  i, 
but  at  the  instant  contact  is  broken  between  a  and  i  a  pronounced  spark 
appears. 


FIG.  249. — Multiple  gap  and  multiple  contact  pole-changer. 

In  the  first  case  the  "make"  spark  which  develops  is  due  to  the  dis- 
charge of  the  circuit  possessing  capacity,  and  in  the  second  case  the  spark 
observed  is  due  to  the  extra  current  of  self-induction. 


DUPLEX  TELEGRAPHY 


285 


It  should  be  remembered,  of  course,  that  when  arcing  takes  place  be- 
tween the  contact  points  of  a  pole-changer,  the  arc  is  the  result  of  difference 
of  potential  between  the  battery  terminals  of  the  instrument,  and  that  the 


FIG.  250. — Multiple  contact  pole-changer  employing  three  transmitters. 

only  part  played  by  the  make  or  the  break  spark  when  an  arc  is  " struck" 
is  that  of  reducing  the  resistance  of  the  air-gap  to  a  degree  which  permits 
the  formation  of  the  arc.  The  heat  of  the  arc  which  ranges  from  2,000  to 
5,000°  C.  is  very  destructive  to  the  metallic  terminals. 


FIG.  251.— The  Field  multiple-gap  pole-changer. 

The  ordinary  make  and  break  sparks,  if  excessive  are  liable  to  heat  the 
air  of  the  gap  (thus  reducing  its  electrical  resistance)  to  a  point  where 
arcing  is  likely  to  occur. 

In  place  of  the  shunt  discharge  path,  a  plan  has  been  tried  which  con- 
sists of  providing  a  multiple  gap  as  illustrated  in  Fig.  249,  wherein  it  may  be 


286  AMERICAN  TELEGRAPH  PRACTICE 

noted  that  each  dynamo  terminal  is  brought  to  two  separate  contact  points. 
The  armatures  of  two  separate  pole-changers  are  controlled  by  an  individual 
battery  and  key  circuit,  which  when  closed  places  both  armature  levers  in 
contact  with  the  negative  pole  of  the  battery  and  when  opened  places  both 
levers  in  contact  with  the  positive  pole  of  the  battery.  An  instrument 
designed  on  this  principle  is  known  as  the  Berry  pole-changer,  being  the 
invention  of  Mr.  T.  H.  Berry. 

It  is  evident  that  as  each  battery  contact  is  made  at  two  separate  points, 
the  sparking  tendency  at  each  contact  is  halved. 

A  similar  arrangement  employing  three  ordinary  pole-changers  for  the 
purpose  is  illustrated  in  Fig.  250. 

Figure  251  shows  a  pole-changer  having  a  multiple  gap,  which  has  been 
designed  by  Mr.  Stephen  D.  Field. 

In  cases  where  high  potentials  are  employed,  and  where  high  signaling 
speeds  are  not  essential,  the  aoil"  break  has  been  used  with  success.  With 
this  arrangement  the  pole-changer  is  inverted  and  the  contact  between 
armature  and  battery  terminals  is  made  to  take  place  in  a  chamber  filled 
with  thin  oil,  in  which  case  the  oil  serves  to  extinguish  the  spark  as  soon 
as  formed. 


CHAPTER  XIV 
THE  QUADRUPLEX 

THE  JONES  SYSTEM.  THE  FIELD  KEY  SYSTEM.  THE  POSTAL  QUADRUPLEX. 
THE  SINGLE  DYNAMO  QUADRUPLEX.  THE  METALLIC -CIRCUIT  QUAD- 
RUPLEX. THE  GERRITT  SMITH  QUADRUPLEX.  THE  WESTERN  UNION 
QUADRUPLEX.  THE  B.P.O.  QUADRUPLEX. 

Quadruplex  telegraphy  consists  of  a  method  of  sending  two  messages 
simultaneously  over  an  individual  wire  in  one  direction,  while  at  the  same 
time  two  additional  messages  are  being  transmitted  over  the  same  wire  in 
the  opposite  direction. 

A  wire  equipped  at  each  end  with  quadruplex  apparatus  may  be  used  to 
transmit  one,  two,  three,  or  four  telegrams  at  the  same  time.  That  is,  when 
the  wire  is  equipped  for  quadruplex  working,  one  message  at  a  time  may  be 
sent  over  it,  or,  if  required,  four  telegrams  (two  in  each  direction)  may  be 
transmitted  simultaneously. 

The  system  of  quadruplex  telegraphy  generally  employed  is  based  on  a 
combination  of  the  Stearns,  or  single-current  duplex,  and  the  differential 
polar  duplex,  both  of  which  have  been  described  in  the  preceding  chapter. 

One  message  in  each  direction  may  be  transmitted  by  means  of  the 
single-current  half  of  the  system  due  to  changes  effected  in  the  strength  of 
the  line  currents  without  regard  to  the  polarity  of  said  currents,  while  one 
message  in  each  direction  may  at  the  same  time  be  transmitted  by  means 
of  the  polar  half  of  the  system  due  to  alterations  in  the  polarity  of  currents 
impressed  upon  the  line,  which  alterations  are  effected  through  the  agency 
of  ordinary  transmitting  keys  and  pole-changers  as  described  in  connection 
with  the  differential  polar  duplex  system. 

Figure  252  shows  the  theoretical  wiring  of  the  main-line  circuits,  and  the 
pole-changer  and  transmitter  local  circuits  of  a  quadruplex  arranged  to 
operate  with  gravity  battery.  In  the  diagram  the  circuit  arrangements 
at  two  terminal  stations  are  shown,  the  two  stations  X  and  Y  being  connected 
by  a  line  wire. 

For  the  sake  of  clearness  the  reading  sounder  circuits  which  are  operated 
locally  through  the  action  of  the  armatures  of  the  polar  relays  and  the  neu- 
tral relays  have  been  omitted.  The  letters  o  and  c,  however,  are  used  as 
indices  to  denote  the  open  and  the  closed  positions  of  the  respective  relay 
armatures.  In  each  case  the  closed  position  of  the  relay  armature  implies 
that  the  signaling  armature  lever  of  the  reading  sounder  connected  thereto 
would  also  be  in  the  closed  or  marking  position. 

287 


288 


AMERICAN  TELEGRAPH  PRACTICE 


It  is  to  be  remembered  that  the  armature  of  the  polar  relay  will  be  drawn 
into  the  closed  position  when  current  traverses  the  coil  windings  of  the  relay 
in  a  given  direction,  and  into  the  open  position  when  current  travels  through 
the  coils  in  the  reverse  direction.  It  is  immaterial  whether  the  respective 
currents  are  weak  or  strong.  A  weak  negative  current,  for  instance,  will 


cause  the  armature  to  move  in  one  direction,  while  a  weak  positive  current 
will  cause  the  armature  to  move  in  the  opposite  direction. 

Polar  relays  work  satisfactorily  with  currents  varying  from  3  milliamperes 
to  200  milliamperes,  which  means  that  although  the  movement  of  the  armature 
in  one  direction  may  be  the  result  of  a  strong  positive  impulse,  the  armature 


THE  QUADRUPLEX  289 

may  be  moved  in  the  opposite  direction  by  a  weak  negative  impulse,  pro- 
vided, of  course,  that  the  positive  current  has  been  disconnected  or  sup- 
pressed. Also,  it  will  at  once  be  apparent  that  should  a  wire  carrying  a 
current  of,  say,  50  milliamperes  from  a  positive  source  be  connected  to  one 
terminal  of  the  coil  winding  of  the  relay,  while  a  wire  carrying  a  current  of 
55  milliamperes  from  a  negative  source  is  connected  to  the  other  terminal,  the 
surplus  of  5  milliamperes  negative  current  would  be  sufficient  t>  move  the 
armature  in  the  direction  which  a  negative  current  of  any  strength  would 
move  it.  Further,  as  stated  in  connection  with  the  operation  of  the  relay 
used  in  the  polar  duplex,  the  armature  tongue  of  the  relay,  due  to  the  attrac- 
tion of  the  permanent  magnets  associated  therewith,  remains  in  connection 
with  the  open  or  the  closed  contact  once  it  has  been  moved  there,  until  the 
direction  of  the  current  through  the  coils  of  the  instrument  has  been  reversed, 
whereupon  the  tongue  instantly  moves  over  to  the  opposite  contact. 

That  half  of  the  quadruplex  which  is  operated  by  means  of  current  re- 
versals is  called  the  polar,  A,  or  first  side  of  the  system,  while  the  half  which 
is  operated  by  raising  and  lowering  the  strength  of  the  current  obtaining  in 
the  main-line  circuit  is  called  the  neutral,  common,  B,  or  second  side  of  the 
system. 

THE  DIFFERENTIAL  NEUTRAL  RELAY 

The  description  of  the  differential  relay  given  on  page  251  applies  equally 
to  the  type  of  relay  employed  on  the  second  side  of  the  differential  quadruplex 
to  record  the  signals  transmitted  from  the  distant  station  as  a  result  of  the 
operation  of  the  transmitter  connected  into  the  line  at  that  point,  and  by 
means  of  which  the  strength  of  current  permitted  to  traverse  the  line  is 
regulated. 

The  forward  and  backward  movements  of  the  armature  of  the  neutral 
relay  are  accomplished  in  a  manner  somewhat  different  from  that  which  actu- 
ates the  armature  of  the  polar  relay.  The  armature  tongue  of  the  neutral 
relay  is  drawn  into  contact  with  its  back-stop  by  the  action  of  a  retractile 
spring  which  may  be  given  a  tension  such  that  a  comparatively  large  volume 
of  current  must  traverse  one  or  both  coils  of  the  relay  before  the  armature 
will  be  attracted  forward.  Also,  as  is  the  case  with  the  ordinary  or 
common  single  Morse  relay,  it  is  immaterial  whether  the  current  traversing 
the  coil  windings  of  the  relay  is  from  a  positive  or  a  negative  source,  provided 
the  current  actuating  the  magnets  has  the  required  strength  to  overcome 
the  spring  tension  which  tends  to  hold  the  armature  tongue  against  its 
back-stop. 

Thus  it  is  seen  that  if  the  current  operating  the  polar  side  of  the  system 
is  kept  down  to  a  strength  of,  say,  2  5  milliamperes,  the  retractile  spring  of  the 
companion  neutral  relay  may  be  given  a  tension  which  will  prevent  it  from 
responding  to  currents  of  such  comparatively  low  volume. 

19 


290 


AMERICAN  TELEGRAPH  PRACTICE 


It  is  customary  to  so  adjust  the  neutral  relay  that  a  current  strength 
three  times,  or  four  times,  greater  than  that  which  operates  the  polar  relay 
must  be  impressed  upon  the  line  before  the  neutral  relay  will  respond.  As 
long,  therefore,  as  the  neutral  side  transmitter  at  the  distant  station  is  not 
operated,  and  while  minimum  current  value  obtains  in  the  main-line  circuit, 
although  the  polar  side  may  be  operated,  the  neutral  relay  remains  unrespon- 
sive. The  instant,  however,  that  the  neutral  side  transmitter  at  the  distant 
station  is  closed,  maximum  current  value  obtains  in  the  main-line  cir- 
cuit and  the  neutral  relay  at  the  home  station  instantly  responds. 

The  various  electrical  actions  which  take  place  when  full  quadruplex 
operation  is  maintained  over  a  wire  are  directly  dependent  upon  the  differ- 
ence of  potential  existing  between  certain  points  in  the  main-line  circuit 

A 


C  R.  200  Ohms     KR.  200  Ohms 


FIG.  253  — The  Diplex. 

within  the  apparatus  at  each  end  of  the  line,  upon  the  resistance  of  instrument 
windings  and  accessory  resistance  units,  and  upon  the  direction  and  strength 
of  currents  flowing  through  relay  windings  at  certain  instants  and  under 
certain  conditions. 

Most  students  find  it  difficult  to  carry  in  their  minds  a  picture  of  the  many 
operations  taking  place  which,  taken  all  together,  constitute  quadruplex  work- 
ing. But,  if  the  subject  is  approached  with  a  view  to  mastering  each  detail 
of  operation  separately,  it  is  found  generally  that  when  the  various  details 
are  understood,  the  theory  of  the  system  as  a  whole  will  be  more  firmly 
impressed  upon  the  mind  than  if  this  method  of  study  were  not  followed. 

We  have  seen  in  the  case  of  the  Stearns  duplex,  the  polar  duplex  and  the 
bridge  duplex,  that  two  messages  at  a  time  may  be  sent  over  a  single  wire, 
one  in  each  direction.  In  order  to  maintain  quadruplex  operation,  means 
must  be  provided  for  transmitting  four  messages  at  a  time  over  a  single 
wire,  two  in  each  direction. 

It  will  be  helpful ;  first  to  consider  an  arrangement  such  as  that  illustrated 
in  Fig.  253,  by  means  of  which  it  is  possible  to  transmit  two  messages  simul- 
taneously over  a  single  wire,  both  in  one  direction.  This  provides  what  was 
at  one  time  known  as  diplex  operation. 

As  transmission  is  carried  on  in  one  direction  only,  one  station  is  equipped 


THE  QUADRUPLEX  291 

with  sending  apparatus,  while  the  other  station  is  equipped  with  receiving 
apparatus  only. 

The  particular  arrangement  of  circuits  depicted  in  Fig.  253  is  submitted 
here;  not  that  it  closely  resembles  the  circuit  arrangements  comprising  the 
diplex  system  of  telegraphy  originally  introduced,  but  because  it  embodies 
features  common  to  the  present-day  system  of  quadruplex  telegraphy  which 
make  possible  the  simultaneous  transmission  of  two  messages  in  each  direc- 
tion over  a  single  wire. 

A  line  wire  having  an  assumed  resistance  of  1,800  ohms  is  shown  extend- 
ing between  stations  A  and  B,  the  direction  of  transmission  being  from  A  to 
B.  The  main  battery  consisting  of  gravity  cells,  having  a  total  e.m.f.  of- 
200  volts  and  an  internal  resistance  of  400  ohms  is  located  at  A,  as  also  is 
the  pole-changer  PC,  operated  locally  by  means  of  a  key  K,  and  the  trans- 
mitter r,  the  latter  in  this  case  consisting  simply  of  a  key  Kz  which,  when 
open  places  the  3,ooo-ohm  shunt  coil  r  in  series  with  the  line  wire,  and  when 
closed  short  circuits  this  coil. 

At  the  receiving  end  of  the  line  two  relays  are  connected  directly  into  the 
main-line  circuit  as  shown.  One  of  these — the  polar  relay  PR — is  actuated 
by  current  reversals,  that  is,  its  armature  is  moved  into  the  closed  posi- 
tion when  the  negative  terminal  of  the  distant  battery  is  placed  to  line,  and 
into  the  open  position  when  the  positive  terminal,  or  pole,  of  the  distant 
battery  is  placed  to  line. 

The  operation  of  the  common  relay  CR  is  dependent  upon  the 
strength  of  the  current  traversing  its  coils,  and  not  upon  the  direction  of 
current. 

By  referring  to  the  diagram  it  may  be  seen  that  at  the  sending  station  the 
key  K  is  depressed.  This  action  has  moved  the  spring  contact  A  away  from 
the  line  contact-block  c,  with  the  result  that  the  positive  terminal  of  the 
battery  is  connected  to  ground  via  the  key  K,  while  the  negative  terminal 
of  the  battery  is  placed  to  line  by  way  of  spring  contact  B  and  line  contact- 
block  c,  from  which  point  the  main-line  circuit  to  ground  at  the  distant  sta- 
tion is  made  up  via  the  3,ooo-ohm  coil  r  (Key  K^  now  being  open)  the  1,800- 
ohm  line  wire  through  the  windings  of  the  polar  relay  and  the  common 
relay,  thence  to  ground. 

Calculation  will  show  that  the  current  strength  obtaining  in  the  circuit 
is  about  36  milliamperes.  And  if  it  is  assumed  that  the  spring  S  attached  to 
the  armature  of  the  common  relay  has  been  given  a  tension  such  that  a 
current  strength  considerably  in  excess  of  36  milliamperes  must  obtain  in  the 
circuit  before  the  armature  of  the  relay  is  attracted,  it  is  plain  that  the  opera- 
tion of  the  pole-changer  at  the  sending  station  will  have  no  effect  upon  the 
common  relay,  while  on  the  other  hand,  the  armature  of  the  polar  relay  is 
moved  into  the  closed  position  each  time  a  negative  current  is  sent  to  line,  and 
into  the  open  position  each  time  a  positive  current  is  sent  to  line  from  the 


292  AMERICAN  TELEGRAPH  PRACTICE 

distant  station.  It  must  be  kept  in  mind,  as  pointed  out  elsewhere,  that 
the  polar  relay  responds  to  very  low  current  strengths. 

Now,  if  key  K2  is  depressed,  thus  short  circuiting  the  3,ooo-ohm  coil  r, 
a  strength  of  current  will  obtain  in  the  circuit  which  is  about  three  times 
greater  than  that  which  existed  while  the  key  K2  remained  open.  • 

It  is  self-evident,  therefore,  that  the  operation  of  the  key  K2  controls 
the  movements  of  the  armature  of  the  common  relay,  while  the  operation 
of  the  key  K  controls  the  operation  of  the  polar  relay. 

DOUBLE  TRANSMISSION  IN  BOTH  DIRECTIONS 

Having  an  apparatus  such  as  the  diplex  by  means  of  which  two  sets  of 
signals  may  be  sent  in  the  same  direction  over  a  single  conductor  without 
interference  with  each  other,  it  is  evident  that  by  employing  differentially 
wound  relays  at  each  end  of  the  line,  placing  one  winding  of  each  relay  in 
the  main-line  circuit  while  the  other  winding  of  each  relay  is  included  in  the 
artificial-line  circuit,  as  is  done  in  the  case  of  the  Stearns  and  polar  duplexes, 
it  is  possible  to  transmit  two  messages  in  each  direction  simultaneously. 

THE  GRAVITY  BATTERY  QUADRUPLEX 

Figure  254  shows  theoretically  the  main-line  circuits  of  a  quadruplex 
operated  with  current  derived  from  a  gravity  battery.  The  type  of  pole- 
changer  shown  here  is  different  from  that  illustrated  in  connection  with  Fig. 


FiG^  254. — Postal  Telegraph  Company's  gravity  battery  quadruplex.     Theory. 

252  (see  also  Fig.  255)  and  consists  of  two  double-contact  relays  of  the  usual 
construction. 

.In  practice  an  individual  sending  key  connected  through  a  local  battery 
controls  the  operation  of  both  of  the  instruments  comprising  the  pole-changer. 
By  this  means,  when  the  key  is  depressed  both  armatures  of  the  pole-changer 


THE  QUADRUPLEX 


293 


relays  are  attracted  into  contact  with  their  front-stops,  and  when  the  key 
is  opened  both  armatures  are  withdrawn  into  contact  with  their  back-stops, 
due  to  the  tension  of  the  retractile  springs  attached  to  them  for  that  purpose. 
It  may  be  noted  that  the  function  of  the  armature  of  the  instrument  on 
the  right  is  to  "ground"  either  pole  of  the  main  battery,  while  the  function 
of  the  armature  of  the  instrument  on  the  left  is  to  place  to  line  that  pole 
of  the  battery  which  is  not  grounded.  The  pole  of  the  battery  which  is 
grounded  and  the  pole  which  is  to  line  at  any  given  instant  depends  upon  the 
positions  of  the  respective  armatures.  When  the  signaling  key  is  closed, 
both  armature  tongues  will  be  in  contact  with  their  front-stops.  In  the 
case  before  us  this  action  has  placed  the  negative  pole  of  the  battery  to  the 
line,  while  the  positive  pole  of  the  battery  is  grounded.  On  the  other  hand, 


FIG.  255. — Pole-changer  or  transmitter.     Postal  pattern. 

when  the  signaling  key  is  opened,  the  positive  terminal  of  the  battery  will 
be  placed  to  line  while  the  negative  pole  will  be  grounded.  Thus,  it  is  seen 
that  the  operation  of  the  signaling  key  controlling  individually  the  movements 
of  the  two  armatures  results  in  currents  being  sent  to  line  which  alternate 
in  polarity. 


THE  TRANSMITTER 

The  position  of  the  armature  of  the  transmitter  J1,  at  any  given  instant 
determines  whether  the  whole  or  a  portion  only  of  the  main  battery  is  utilized. 
By  observing  the  two  possible  positions  of  the  transmitter  armature  it  will 
be  evident  that  when  the  signaling  key  which  controls  the  operation  of  the 
transmitter  is  depressed,  the  armature  tongue  will  be  moved  into  contact 
with  its  front-stop  thereby  opening  the  "tap"  connection  and  placing  the 
entire  battery  in  service.  When,  on  the  other  hand,  the  key  is  opened  and 
the  armature  tongue  is  withdrawn  into  contact  with  its  back-stop,  one-third 
or  one-fourth,  as  the  case  may  be,  of  the  main  battery  is  availed  of. 


294 


AMERICAN  TELEGRAPH  PRACTICE 


>1 

G 
rt 

O, 

<§ 

44 

a 
2 

I 

H 


sed 


quad 


THE  QUADRUPLEX  295 

LONG  END  AND  SHORT  END 

When  the  armature  of  the  transmitter  is  in  the  position  which  places  the 
entire  battery  in  service,  it  is  said  that  the  long  end  is  to  line,  and  when  the 
armature  of  the  transmitter  is  in  the  opposite  position,  that  is,  when  a  part 
of  the  battery  is  utilized,  it  is  said  that  the  short  end  of  the  battery  is  to  line. 

Figure  256  shows  the  actual  binding-post  main-line  connections  of  a 
battery  quadruplex,  the  theoretical  wiring  of  which  is  shown  in  Fig.  254. 
In  the  actual  instrument  connections  the  artificial  line  is  made  up  of  an 
adjustable  rheostat  and  two  3-m.f.  condensers,  the  latter  also  being 
adjustable. 

THE  DYNAMO  QUADRUPLEX 

THE  JONES  SYSTEM 

The  distinguishing  feature  of  the  Jones  dynamo  quadruplex  is  the  method 
employed  to  furnish  the  long-end  and  the  short-end  main-line  potentials. 
By  referring  to  diagram  257,  it  may  be  seen  that  four  separate  dynamos  are 
required  to  furnish  the  desired  potentials — two  130- volt  machines  and  two 
385-volt  machines.  The  130  volts  plus  and  minus  serving  as  the  reduced 
potential,  while  the  higher  voltage  serves  as  the  full  potential  to  operate  the 
neutral  relay  at  the  distant  end  of  the  line. 

In  the  diagram  the  polar-side  transmitting  key  KI  is  shown  in  the  closed 
position,  the  result  of  which  is  that  the  armature  levers  of  the  two  instru- 
ments comprising  the  pole-changer  are  in  contact  with  their  front-stops. 
This  in  turn  connects  the  i3o-volt  negative  potential  and  the  385-volt 
negative  potential  with  the  back-stop  and  front-stop  respectively  of  the 
transmitter  T.  It  is  plain  then,  that  as  long  as  the  key  KI  is  kept  closed, 
closing  key  K2  sends  to  line  full  current  strength,  while  opening  key  Kz 
thereby  placing  the  armature  of  the  transmitter  in  contact  with  its  back-stop 
sends  to  line  a  current  of  a  strength  approximately  one-third  of  that  sent 
out  when  the  transmitter  armature  is  in  the  closed  position. 

Where  the  booster  arrangement  (see  Fig.  45,  page  63)  for  supplying 
quadruplex  potentials  is  installed,  the  Jones  quadruplex  system  may  be 
employed  to  advantage. 

THE  FIELD  KEY  SYSTEM1 

With  the  Jones  quadruplex  it  is  necessary  to  employ  two  different  e.m.fs., 
one  to  operate  the  polar  and  one  to  operate  the  neutral  side  of  the  system. 

1  The  first  practical  application  of  the  dynamo  as  a  substitute  for  the  chemical  battery 
in  the  operation  of  telegraph  lines  was  made  in  the  year  1879  by  Mr.  Stephen  D.  Field, 
then  of  San  Francisco.  (See  U.  S.  patents,  Nos.  223,845,  Jan.  27,  1880,  and  243,698, 
July  5,  1881.) 


296 


AMERICAN  TELEGRAPH  PRACTICE 


THE  QUADRUPLEX 


297 


As  the  current  strength  required  to  operate  the  latter  compared  with  that 
required  to  operate  the  polar  side  is  in  ratio  3  to  i ,  or  4  to  i ,  as  the  case  may 
be,  it  is  evident  that  with  the  Jones  system  four  sources  of  e.m.f.  are  required, 
two  of  the  higher  value,  one  being  negative  and  the  other  positive,  and  two 
of  the  lower  value,  negative  and  positive.  It  is,  of  course,  understood 
that  while  four  dynamos  are  required  to  operate  one  quadruplex,  the 
same  four  machines  may  at  the  same  time  be  employed  to  supply  current 
for  a  number  of  similar  quadruplex  circuits. 

Where  the  Field  quadruplex  system  is  employed  the  number  of  dynamos 
required  is  reduced  one-half,  as  two  machines  only  are  needed,  one  delivering 
positive  and  the  other  negative  current.  Each  dynamo  delivers  an  e.m.f.  of 
sufficient  strength  to  operate  the  neutral  side,  and  by  employing  properly 
proportioned  resistances  the  insertion  of  which  is  automatically  controlled 
by  operating  the  transmitting  key  associated  with  the  second  side,  the  poten- 


Line 


Condenser 


FIG.  258.— Theory  of  the  Field  quadruplex. 

tial  may  be  reduced  to  a  value  suitable  to  operate  the  polar  side  of  the  system. 
In  this  manner  is  produced  what  has  heretofore  been  referred  to  as  the  "long 
end"  and  the  "short  end." 

The  ratio  of  "long-end"  to  "short-end"  e.m.f.  determines  the  ratio  of 
maximum  to  minimum  line  current,  and  the  novelty  of  the  Field  key  quadru- 
plex, is  in  the  arrangement  of  voltage-reducing  resistances  which  not  only 
provide  for  the  sending  out  of  the  two  properly  proportioned  current  strengths, 
but  at  the  same  time  insure  that  the  whole  or  joint-resistance  of  the  terminal 
circuits  remains  the  same  regardless  of  the  position  of  the  armature  of  the 
transmitter  controlling  the  strength  of  currents  sent  to  line. 

Figure  258  shows  the  theoretical  main-line  wiring  of  the  Field  quadru- 
plex. With  the  armatures  of  the  pole-changer  and  the  transmitter  in  the 
positions  shown  in  the  diagram,  the  completed  circuit  extends  from  the  385- 
volt  -dynamo  to  the  closed-contact  of  the  pole-changer,  thence  via  the  arma- 
ture of  the  pole-changer  along  a  short  connecting  wire  to  the  closed-contact 
of  the  transmitter,  from  which  point  the  circuit  extends — by  way  of  the 


298  AMERICAN  TELEGRAPH  PRACTICE 

armature  of  the  transmitter — to  the  "split"  or  joint-circuit  made  up 
through  the  differential  windings  of  the  two  relays,  half  of  the  current 
reaching  the  earth  via  one  winding  of  each  relay  and  the  artificial-line 
rheostat,  while  the  other  half  reaches  the  earth  at  the  distant  station  via 
the  companion  windings  of  the  relays,  the  line  wire,  and  the  distant  end 
apparatus,  that  is,  the  current  divides  equally  when  the  resistance  of  the 
rheostat  is  made  to  equal  the  resistance  of  the  line  wire  plus  the  resistance 
of  the  terminal  apparatus  at  the  distant  station. 

It  is  apparent,  owing  to  the  shunt  circuit  established  around  the  1,200- 
ohm  added  resistance  by  the  transmitter  armature,  that  the  only  appreciable 
resistance  inserted  before  the  differential  circuit  is  reached  is  that  of  the 
internal  resistance  unit  (in  this  case  having  a  value  of  600  ohms)  connected 
into  the  battery  lead  between  the  dynamo  and  the  pole-changer,  and  which 
serves  to  protect  the  machine  in  case  of  accidental  short-circuit. 

It  is  evident,  too,  with  the  armatures  of  the  pole-changer  and  the  trans- 
mitter in  the  positions  shown,  that  the  nearest  ground  contact  is  at  the  dis- 
tant station  and  at  the  end  of  the  home  artificial-line  rheostat  circuit,  each 
ground  being  equally  distant  ohmically  when  the  resistance  of  the  artificial- 
line  circuit  is  made  to  equal  the  resistance  of  the  circuit  to  ground  at  the 
distant  station. 

As  long,  therefore,  as  the  transmitter  armature  remains  in  the  closed 
position  the  full  potential  of  the  dynamo  is  impressed  upon  the  line,  and 
the  operation  of  the  pole-changer  results  in  positive  and  negative  currents 
of  maximum  strength  being  sent  to  line  as  the  armature  tongue  of  the  pole- 
changer  is  moved  into  contact  with  the  open  or  closed  contact  respectively. 

Assume  now  that  the  key  circuit  controlling  the  operation  of  the  trans- 
mitter is  opened,  permitting  the  retractile  spring  to  withdraw  the  armature 
into  contact  with  its  back-stop,  it  will  be  seen  that  the  nearest  ground  con- 
tact is  distant  in  ohms  from  the  source  of  e.m.f.  600  ohms  (internal),  plus 
1,200  ohms  (added),  plus  900  ohms  (leak),  or  2,700  ohms;  and  further,  that 
the  point  X  is  two-thirds  of  the  distance  (ohmically)  to  the  nearest  ground, 
for,  600  plus  1,200  is  two-thirds  of  2,700.  This  means  that  at  the  point  X, 
while  the  transmitter  armature  tongue  is  in  contact  with  its  back-stop,  the 
voltage  has  dropped  from  385  to  one-third  of  385,  or  omitting  fractions, 
1 28  volts.1 

With  these  particular  values  of  added  and  leak  resistances  we  have  a 
ratio  of  3  to  i,  with  a  long-end  potential  of  385  volts  and  a  short-end  potential 
of  128  volts,  the  former  being  impressed  on  the  line  when  the  armature 
tongue  of  the  transmitter  is  in  contact  with  its  front-stop,  and  the  latter 
when  the  tongue  is  in  contact  with  its  back-stop.  This  in  turn  insures 
that  maximum  current  will  obtain  in  the  main-line  circuit  while  the  signal- 

1  See  Fall  of  Potential  in  an  Electric  Circuit,  page  88. 


THE  QUADRUPLEX  299 

ing  key  which  controls  the  operation  of  the  transmitter  is  closed,  and  that 
minimum  current  will  obtain  in  the  main-line  circuit  while  the  same  key  is 
open.  The  result,  therefore,  is  that  closing  the  transmitter  key1  causes  a 
current  volume  in  the  main-line  circuit  of  sufficient  strength  to  attract  the 
armature  of  the  neutral,  or  common-side  relay  at  the  distant  station,  while 
opening  the  transmitter  key  circuit  results  in  the. main-line  current  strength 
being  so  reduced  that  the  armature  of  the  distant  neutral  relay  is  withdrawn 
from  the  closed  position  due  to  the  tension  of  the  retractile  spring  attached 
to  it. 

So  far  as  the  operation  of  the  neutral  relay  at  the  distant  station  is  con- 
cerned it  is  immaterial  whether  the  armature  of  the  home  pole-changer  is 
in  contact  with  the  +385-volt  dynamo  or  the  —  385-volt  dynamo,  as  the 
neutral  relay  responds  to  either  polarity,  provided  maximum  current  strength 
obtains  in  the  main-line  circuit. 

The  operation  of  the  polar  relay  at  the  distant  station  being  dependent 
upon  current  reversals,  regardless  of  the  strength  of  the  current,  is  as  a  conse- 
quence under  the  control  of  the  home  pole-changer.  As  long  as  the  armature 
tongue  of  the  home  pole-changer  remains  in  contact  with  the  negative  battery 
connection,  the  armature  of  the  polar  relay  at  the  distant  office  will  be  in 
one  position,  and  as  long  as  the  armature  of  the  pole-changer  is  in  contact 
with  the  positive  battery  connection  the  armature  of  the  distant  polar  relay 
will  remain  in  the  opposite  position. 

METHOD   OF  DETERMINING   THE    REQUIRED    OHMIC  VALUE  OF  RESIS- 
TANCE COILS  TO  USE  IN  THE  FIELD  KEY  SYSTEM  TO  OBTAIN 
ANY  DESIRED  PROPORTION 

Instead  of  a  current  ratio  of  3  to  i,  it  is  sometimes  advisable  to  maintain 
a  ratio  of  3  1/2  to  i,  or  4  to  i,  etc. 

Convenient  and  simple  formulae,  for  determining  the  values  of  the  added 
and  leak  resistances  for  any  given  ratio  are  given  herewith, 

where  R,  represents  ratio, 

B,  represents  internal  resistance, 
RI,  represents  added  resistance, 
R2,  represents  leak  resistance, 

BR 
then  R->  =  -^ 


or 


2 

=  B  (R-i) 


- 

For  the  sake  of  clearness  the  transmitter  local  key  circuit  has  been  omitted. 


300  AMERICAN  TELEGRAPH  PRACTICE 

The  value  of  the  internal  resistance  is  usually  selected  with  regard  to 
the  measure  of  protection  to  be  given  the  generators,  and  in  practice  may  be 
600,  300,  200,  100  ohms,  or  less. 

Suppose,  for  instance,  that  with  an  internal  resistance  of  600  ohms  a 
certain  circuit  is  to  be  operated  on  a  3  to  i  basis: 

R,  has  a  value  of  3, 
B,  a  value  of  600,  then 

added  resistance  =  600 X  (3  —  i)  =  1,200  ohms 

leak  resistance  = -  =  900  ohms,  or  the  same  as  the 

3-i 

values  indicated  in  Fig.  258. 

When  the  values  of  the  internal,  leak,  and  added  resistances  are  known, 
the  ratio,  according  to  the  formula,  would  be 

600+900+1200  _ 
900  ~^ 

To  ascertain  the  value  of  the  potential  at  the  pointZ  (Fig.  258)  with  any 
given  combination  of  added  resistance,  the  following  formula  applies: 

y    E  (R-RJ 
R 

where  E  represents  the  voltage  of  the  generator, 

R  represents  the  resistance  of  the  whole  circuit  to  the  nearest 

ground, 

RI  represents  the  point  distant  in  ohms  from  the  source  of 
e.m.f. 

With  the  resistance  values  shown  in  Fig.  258, 


X  =  ^          -=128  1/3  volts. 
2700 

By  the  aid  of  the  foregoing  formulae,  the  subjoined  table  has  been  com- 
piled showing  the  added  and  leak  resistance  values  required  with  ratios  of 
3-1,  3.5-1,  and  4-1,  with  internal  resistance  values  ranging  from  50  to 
1,000  ohms. 


THE  QUADRUPLEX 

ADDED  AND  LEAK  RESISTANCE 


301 


3  t 

D  I 

3-5 

to  i 

4   t 

3  I 

Internal 

resistance 

Added 

Leak 

Added 

Leak 

Added 

Leak 

5o 

IOO 

75 

125 

70 

150 

67 

TOO 

200 

J5o 

250 

140 

300 

133 

200 

4OO 

300 

500 

280 

600 

267 

300 

6OO 

45o 

750 

420 

900 

400 

400 

800 

600 

1,000 

560 

1,200 

533 

500 

,OOO 

750 

1,250 

700 

1,500 

667 

600 

,200 

900 

1,500 

840 

i,  800 

800 

700 

,4OO 

1,050 

i,75° 

980 

2,100 

933 

800 

,60O 

1,200 

2,000 

I,I2O 

2,400 

1,067 

QOO 

,800 

i,3So 

2,250 

I,26o 

2,700 

1,200 

I,OOO 

2,OOO 

1,500 

2,500 

I,40O 

3,000 

1,333 

TERMINAL  RESISTANCE 

It  is  necessary  that  the  whole  or  joint-resistance  of  the  terminal  apparatus 
remain  the  same  regardless  of  the  position  of  the  armature  of  the  transmitter 
at  any  instant.  That  this  is  important  is  evident  from  the  fact  that  in  the 
act  of  balancing,  the  distant  station  adjusts  the  resistance  of  the  artificial-line 
rheostat  to  equal  the  resistance  of  the  line  plus  the  resistance  of  the  apparatus 
at  the  other  end  of  the  line.  Therefore,  after  the  balance  has  been  taken  the 
same  value  should  at  all  times  be  maintained,  else  the  outgoing  currents  will 
not  have  identical  values  in  the  separate  windings  of  the  relays. 

Figure  259  shows  the  resistance  values  of  the  various  elements  of  a  quad- 
ruplex  set  at  each  end  of  a  line  extending  between  stations  Y  and  Z,  assum- 
ing a  line  conductor  resistance  of  2,000  ohms,  an  internal  resistance  of  600 
ohms  in  each  dynamo  lead,  a  long-end  potential  of  385  volts,  and  a  ratio  of 
long  to  short  e.m.f.  of  3  to  i. 

It  may  be  observed  that  the  resistance  of  the  terminal  apparatus  at  each 
station  remains  the  same  at  all  times.  With  the  armatures  of  the  pole- 
changer  and  the  transmitter  in  the  positions  shown  in  the  diagram  the  only 
appreciable  resistance  presented  to  incoming  currents  at  station  Z  (in  addi- 
tion to  the  relay  resistance)  is  the  6oo-ohm  internal  resistance  B,  as  it  is 
plain  that  the  1,200  ohms  added  resistance  is  short  circuited  by  virtue  of  the 
closed  position  of  the  transmitter  armature.  Should  the  pole-changer  key 
be  opened  so  that  the  armature  tongue  of  the  latter  is  withdrawn  into  contact 
with  its  back-stop  there  is  still  presented  a  6oo-ohm  path  to  ground. 


302  AMERICAN  TELEGRAPH  PRACTICE 

Referring  now  to  the  conditions  prevailing  at  station  F:  At  first  sight 
it  would  seem  that  owing  to  the  armature  tongue  of  the  transmitter  being 
in  contact  with  its  back-stop,  a  path  is  presented  to  incoming  signals  which 
has  a  resistance  considerably  higher  than  that  which  obtains  when  the  arma- 
ture is  in  the  closed  position,  but  a  little  consideration  will  show  that  with  the 
transmitter  armature  in  the  position  shown  at  F  the  incoming  signals  have  a 
joint  path  from  the  point  X  consisting  of  a  goo-ohm  branch  and  an  1,800- 
ohm  branch,  and  calculation  will  show  that  the  joint-resistance  of  these  two 
paths  is  600  ohms. 

RESISTANCE  OF  THE  "GROUND"  COIL 

When  the  attendant  at  one  end  of  the  quadruplexed  circuit  "  takes  a  line 
balance, "  that  is,  when  he  adjusts  the  resistance  of  the  artificial  line  rheostat 
to  equal  the  resistance  of  the  line  and  of  the  apparatus  at  the  distant  end  of  the 
line,  it  is  necessary  that  the  main-line  battery  at  the  distant  end  of  the  line  be 
removed  until  the  balance  is  taken. 

Assume  that  the  attendant  at  F  (Fig.  259)  is  about  to  take  a  balance. 
In  the  process  of  balancing,  the  attendant  at  Z  is  required  to  "ground"  the 
line  (thereby  removing  the  main-line  battery  at  Z)  by  moving  the  switch 
lever  S  into  contact  with  the  ground  connection.  Inasmuch,  therefore,  as 
the  balance  is  taken  when  a  6oo-ohm  terminal  resistance  is  presented  at  the 
distant  station  it  is  essential  that  when  the  switch  S  is  turned  back  to  the 
regular  position  (thereby  placing  battery  to  line)  the  terminal  resistance 
presented  must  remain  the  same,  namely,  600  ohms,  if  the  balance  is  to  hold 
good  while  the  circuit  is  in  operation. 

The  value  of  the  resistance  of  the  ground  coil  must  be  identical  with  that 
of  the  internal  resistance  By  which  also  is  identical  with  the  joint  resistance 
of  the  terminal  resistance  presented  to  incoming  signals  when  the  armature 
of  the  transmitter  is  in  contact  with  the  leak  circuit. 

Undoubtedly  it  will  have  occurred  to  the  reader  that  the  resistance  of 
the  terminal  apparatus  (600  ohms  in  this  case),  in  reality  forms  one  branch 
of  a  joint  circuit,  the  other  branch  of  which  consists  of  the  3,ioo-ohm  circuit 
to  ground  made  up  via  the  relay  windings  and  the  artificial-line  rheostat,  and, 
of  course,  this  is  true,  for  in  the  case  under  consideration  (Fig.  259)  the  joint 
resistance  of  600  ohms  and  3,100  ohms  is  approximately  503  ohms,  but  it  is 
evident  that  the  3,ioo-ohm  branch  of  the  joint  circuit  formed  a  joint  circuit 
with  the  6oo-ohm  ground  coil  at  the  time  the  balance  was  taken,  so  that  the 
actual  total  resistance  of  the  terminal  apparatus  presented  to  incoming  sig- 
nals is  the  same  regardless  of  the  position  of  the  ground  switch. 

OPERATION  OF  THE  QUADRUPLEX 

If  the  reader  has  mastered  the  principles  of  operation  of  the  Stearns 
duplex  and  of  the  polar  duplex  described  in  Chapter  XIII  he  should  have 


THE  QUADRUPLEX 


303 


N 


CV) 


cr 

TJ 

'w 

E 

0) 

rfl 


304 


AMERICAN  TELEGRAPH  PRACTICE 


little  difficulty  tracing  out  the  various  operations  which  take  place  in  the 
quadruplex  while  two  messages  are  being  transmitted  in  each  direction  at 
the  same  time.  The  method  of  study  which  gives  the  best  results  is  for  the 
student  to  draw  diagrams  showing  the  various  positions  of  the  transmitter 
and  pole-changer  armatures  at  either  end  of  a  quadruplex  circuit  and  from 
these  gain  a  first  hand  knowledge  of  the  operation  of  the  relays  at  each  end 
in  response  to  the  operation  of  the  signaling  keys  at  the  opposite  end  of  the 
circuit. 

In  making  up  diagrams  the  following  schedule  of  combinations  may  be 
used  as  a  guide  in  tracing  the  various  possible  connections : 

/  Home  PC  open,  Distant  PC  open, 
\  Home  T  open,  Distant  T  open. 

Home  PC  closed,  Distant  PC  open, 

Home  T  open,  Distant  T  open. 

Home  PC  open,  Distant  PC  open, 

Home  T  closed,  Distant  T  open. 

Home  PC  closed,  Distant  PC  open, 

Home  T  closed.  Distant  T  open. 

Home  PC  open,  Distant  PC  closed, 

Home  T  open,  Distant  T  open. 

Home  PC  closed,  Distant  PC  closed, 

Home  T  open,  Distant  T  open. 

Home  PC  open,  Distant  PC  closed, 

Home  T  closed,  Distant  T  open. 

Home  PC  closed,  Distant  PC  closed, 

Home  T  closed,  Distant  T  open. 

Home  PC  open,  Distant  PC  open, 

Home  T  open,  Distant  T  closed. 

Home  PC  closed,  Distant  PC  open, 

Home  T  open,  Distant  T  closed. 

Home  PC  open,  Distant  PC  open, 

Home  T  closed,  Distant  T  closed. 

Home  PC  closed,  Distant  PC  open, 

Home  T  open,  Distant  T  closed. 

Home  PC  closed,  Distant  PC  closed, 

Home  T  open,  Distant  T  closed. 

Home  PC  open,  Distant  PC  closed, 

Home  T  closed,  Distant  T  closed. 

Home  PC  closed,  Distant  PC  closed, 

Home  T  closed,  Distant  T  closed. 

THE  DAVIS-EAVES,  OR  POSTAL  QUAD 


14.  < 

„ 


16. 


The  Postal  Telegraph-Cable  Company  has  recently  put  into  service  a 
large  number  of  quadruplex  sets  arranged  as  shown  theoretically  in  Fig.  260. 

It  will  be  recognized  that  the  arrangement  constitutes  an  improved 
Field  quadruplex;  the  new  features  consisting  of  the  5oo-ohm  " bridge" 
coils,  the  bridge-condenser  circuit,  the  " timed"  condenser  circuit  around 


THE  QUADRUPLEX 


305 


4 


20 


306 


AMERICAN  TELEGRAPH  PRACTICE 


the  relays,  the  25,ooo-ohm  leak  circuit  from  line  to  ground,  also  a  reduced 
value  of  internal,  leak,  and  added  resistance. 

It  will  be  noted,  too,  that  the  spark  curbing  device  consists  of  two  i-m.f. 
condensers  shunting  the  pole-changer  battery  contacts  and  provided  with  a 
discharge  path. 

The  functions  of  the  bridge  coils  and  the  condenser  circuits  have  been 
described  in  connection  with  the  high-efficiency  duplex,  Fig.  257,  page  296. 

Owing  to  the  fact  that  the  terminal  resistance  of  the  set  has  been  reduced 
to  300  ohms  in  place  of  the  600  ohms  formerly  used;  that  the  resistance  of 
the  polar  relay  has  been  reduced  from  300  to  200  ohms,  and  that  of  the 


LEAK RHEOSTAT 


TRJUfSfffTTER 


Eta  * 

POLAR  XffZJfY 


MAIN   CIRCUITS 

FIG.  261. — Actual  connections  of  the  "Postal"  quadruplex. 

neutral  relay  from  150  to  60  ohms,  the  total  resistance  of  the  apparatus 
remains  practically  the  same  as  that  of  the  Standard  Field  quadruplex,  and 
inasmuch  as  specially  arranged  paths  have  been  provided  for  induced  line 
disturbances  it  is  not  necessary  to  employ  very  high  potentials  to  override 
line  currents  from  extraneous  sources,  so  that  in  many  instances  it  is  possible 
to  reduce  the  potential  from  385  volts  to  250  volts,  or  less,  and  still  maintain 
satisfactory  quadruplex  operation. 

Figure  261  shows  the  actual  binding-post  connections  of  the  Postal  quad 
including  all  of  the  new  elements  referred  to  above. 

SINGLE  DYNAMO  QUADRUPLEX 

Figure  262  is  a  sketch  of  the  theory  of  the  connections  of  a  single-dynamo 
quadruplex  arranged  with  a  "double-relay"  pole-changer  so  that  one  dynamo 


THE  QUADRUPLEX 


307 


Line 


Cond'r 


300  Ohms 


FIG.  262. — Single  dynamo  quadruplex.     Theory. 


XOE03TAT, 


FIG.  263. — Binding-post  main  line  connections  of  the  single  dynamo  quadruplex. 


Line 


FIG.  264. — Theoretical  connections  of  a  set  arranged  to  be  used  either  as  a  single  dynamo 
quadruplex  or  as  a  double  dynamo  Field  quadruplex. 


308 


AMERICAN  TELEGRAPH  PRACTICE 


will  serve  to  furnish  currents  of  both  polarities,  positive  and  negative,  for 
main-line  purposes.  It  will  be  noted  that  when  the  armatures  of  the  two 
instruments  which  comprise  the  pole-changer,  are  in  contact :  with  their 
front-stops,  the  negative  terminal  of  the  dynamo  is  placed  to  line,  while 
the  positive  terminal  of  the  dynamo  is  grounded.  And,  when  the  respective 
armatures  are  in  contact  with  their  back-stops,  the  positive  terminal  of  the 
dynamo  is  to  line  and  the  negative  terminal  grounded.  Otherwise  the 
connections  of  the  set  are  the  same  as  in  the  standard  Field  quadruplex. 


FIG.  265. — Instrument  binding-post  connections  of  combination  single  dynamo  and  double 

dynamo  quadruplex. 

This  arrangement  is  efficient  and  economical,  but  its  employment  is 
advisable  only  where  constant  quadruplex  service  is  not  required. 

Figure  263  shows  the  actual  main-line  binding-post  connections  of  the 
single-dynamo  quadruplex. 

Figure  264  shows  a  diagram  of  the  required  switching  connections  of  a 
quadruplex  set  wired  to  operate  either  as  a  single-dynamo,  or  as  a  regula- 
tion two-dynamo  quadruplex,  while  Fig.  265  shows  the  actual  instrument 
binding-post  main-line  connections  of  a  set  arranged  to  operate  as  a  single- 
or  a  double-dynamo  quadruplex. 

METALLIC  CIRCUIT  QUADRUPLEX 

Figure  266  shows  the  instrument  and  battery  switchboard  connections 
of  a  quadruplex  set  arranged  for  metallic  circuit  operation. 

The  system  illustrated  is  arranged  so  that  it  may  be  used  for  grounded- 
circuit,  or  metallic-circuit  operation.  Throwing  the  switches  to  the  left 


THE  QUADRUPLEX 


309 


provides  for  metallic-circuit  operation,  and  throwing  the  switches  to  the 
right  provides  for  single-line  grounded  circuit  operation. 

It  happens  sometimes  that  all  of  the  wires  along  a  particular  route  are  so 
affected  by  induction  from  neighboring  high-tension  power  circuits  that 
quadruplex  operation  over  single  grounded  circuits  is  impossible,  or  at  best 
very  unsatisfactory. 

In  such  cases  the  metallic  circuit  quadruplex  (using  two  main-line  wires 
looped)  has  been  found  to  give  satisfactory  results. 


FIG.  266. — Field  quadruplex  arranged  to  be  operated  over  a  ground  return  circuit  or  a 

metallic  circuit. 

THE  NEUTRAL-RELAY  "KICK,"  AND  THE  "BUG-TRAP"  METHOD  OF  COUNTER- 
ACTING ITS  EFFECTS  ON  SOUNDER  SIGNALS 

As  the  student  constructs  diagrams  showing  the  various  positions  of  the 
armatures  of  the  transmitters  and  pole-changers  at  each  end  of  a  quadruplex 
circuit  as  suggested  in  the  schedule  showing  the  sixteen  possible  combinations, 
it  will  very  likely  occur  to  him  that  the  various  battery  and  condenser 
actions  incident  to  the  operation  of  the  four  signaling  keys,  will  result  in 
constantly  recurring  intervals  of  no  magnetism  in  the  cores  of  the  relays. 

So  far  as  the  polar  relay  is  concerned  the  period  of  no  magnetism  is  of  no 
consequence  as  its  armature  is  held  by  a  permanent  magnet  in  the  position 
into  which  it  was  last  moved  due  to  current  in  the  relay  coils,  and  will  remain 
there  until  the  current  flowing  through  the  relay  coils  has  been  reversed. 
Not  so  with  the  neutral  relay,  however,  as  the  armature  of  the  latter  being 
acted  upon  by  a  retractile  spring  is  drawn  away  from  the  electromagnet  and 


310 


AMERICAN  TELEGRAPH  PRACTICE 


the  closed  contact  point  immediately  upon  the  cessation  of  current  in  the  coil 

windings,  or  upon  reduction  of  the  strength  of  current  actuating  the  magnet. 

It  is  understood  that  the  direction  of  the  current  is  reversed  each  time 

the  armature  of  the  pole-changer  is  caused  to  move  from  the  positive  to  the 


negative  battery  contact,  and  vice  -versa.  As  the  armature  of  the  transmitter 
at  Z  (Fig.  267)  is  in  the  closed  position,  the  armature  of  the  neutral  relay 
at  Y  will  be  in  the  closed  position.  If  now  the  pole-changer  at  Z  is  operated, 
the  first  movement  of  its  armature  will  be  from  the  negative  to  the  positive 


THE  QUADRUPLEX 


311 


battery  terminal,  which  results  in  a  reversal  of  the  direction  of  current  in 
the  windings  of  the  relays.  This  change,  of  course,  requires  time,  as  the 
current  due  to  the  negative  battery  must  disappear  and  the  current  due  to  the 
positive  battery  must  build  up  to  the  strength  required  to  hold  the  armature 
of  the  neutral  relay  against  its  front-stop,  and  this  entails  an  interval  during 
which  the  magnets  of  the  neutral  relay  are  not  magnetized.  It  is  evident 
then,  that  at  this  instant  the  armature  of  the  neutral  relay — due  to  the  action 
of  the  retractile  spring — departs  from  its  front-stop. 

Fortunately  this  interval  of  no-magnetism  is  brief,  and  the  armature 
has  time  to  recede  but  a  short  distance  before  the  magnetism  has  again  built 


FIG.  268. — Repeating  Sounder  "bug-trap." 

up  to  the  strength  necessary  to  attract  it,  due  to  current  from  the  opposite 
battery  pole,  which  in  the  interim  has  been  applied  to  the  line.  But,  although 
brief,  the  interval  of  no-magnetism  frequently  is  of  sufficient  duration  to 
cause  a  false  signal  to  be  produced  on  the  reading  sounder  operated  locally 
by  the  tongue  of  the  neutral  relay. 

This  disturbance  is  sometimes  referred  to  as  the  "B  side  kick"  and  its 
objectionable  effects  are  counteracted  by  devices  variously  arranged  and 
known  as  " bug-traps." 

The  Repeating  Sounder. — The  earliest  adopted  method  of  bridging  over 
the  period  of  no-magnetism  was  that  employing  a  "relaying"  or  "repeat- 
ing" sounder,  so  called. 

Figure  268  shows  schematically  the  wiring  of  the  receiving  side  "local" 
circuits  of  a  quadruplex  set  equipped  with  a  repeating  sounder.  It  will  be 
seen  that  the  armature  lever  of  the  reading  sounder  S,  is  in  the  marking 
position  while  the  armature  tongue  of  the  neutral  relay  is  in  contact  with 
its  front-stop,  and  it  is  evident  that  the  armature  of  the  reading  sounder  will 
not  be  released  until  the  armature  of  the  neutral  relay  has  been  drawn  into 
contact  with  its  back-stop.  Obviously,  a  time  element  is  introduced  which 
consists  of  the  time  taken  by  the  relay  tongue  to  traverse  the  gap  maintained 
between  its  front-stop  and  back-stop  plus  the  time  taken  for  the  magnetism 
in  the  sounder  magnets  to  build  up  to  a  strength  sufficient  to  attract  their 
armatures.  The  repeating  sounder  was  purposely  equipped  with  a  heavy 
armature  lever  in  order  that  it  would  possess  considerable  inertia  and  as  a 
result  thereof,  be  slow  acting  as  compared  with  an  instrument  equipped  with 
a  light  lever. 


312  AMERICAN  TELEGRAPH  PRACTICE 

It  was  found  in  practice  that  during  the  period  of  reversal  when  all  other 
conditions  were  favorable  the  tongue  of  the  neutral  relay  had  time  to  travel 
but  a  minute  distance  away  from  its  front-stop  before  being  called  back  by 
the  resumption  of  magnetism  in  the  cores  of  the  magnet. 

It  might  here  be  observed  that  when  the  short-end  is  to  line  at  the  distant 
station,  there  are  no  deleterious  effects  resulting  from  the  reversals  of  polarity 
consequent  to  the  operation  of  the  distant  pole-changer,  as  now  the  armature 
of  the  home  neutral  relay  remains  in  contact  with  its  back-stop  and  the 
armature  of  the  reading  sounder  is  in  the  non-marking  position. 

The  Gerritt  Smith  Arrangement. — The  Gerritt  Smith  neutral  relay 
arrangement  has  in  the  past  been  used  upon  quadruplexes  in  both  Western 
Union,  and  Postal  Telegraph  service,  and  at  the  present  time  is  in  use  on  a 
number  of  quadruplex  sets  on  various  railroad  telegraph  systems.  A  theo- 
retical sketch  of  the  arrangement  is  shown  in  Fig.  269.  In  the  "Postal's" 
service  the  line  coils  were  wound  to  a  resistance  of  150  ohms,  and  the  "extra" 
coil  to  a  resistance  of  400  ohms,  and  as  an  additional  protection  the  Diehl 
bug-trap  (to  be  described  presently)  was  also  employed. 


Line 


FIG.  269.— The  Gerritt  Smith  neutral  relay  arrangement. 

Figure  269  shows  that  in  the  "Smith"  arrangement  two  4oo-ohm  coils 
form  the  "divide"  for  the  main  and  artificial  lines.  The  insertion  of  these 
coils  is  for  the  purpose  of  establishing  a  momentary  difference  of  potential 
through  the  "extra"  coil  and  condenser  circuit  which  is  "bridged"  across 
the  main-line  and  artificial-line  circuits  when  battery  is  applied  at  the 
distant  end  of  the  line.  When  the  resulting  actions  are  traced  it  will  be 
seen  that  while  either  pole  of  the  distant  battery  is  to  line  a  difference  of 
potential  is  established  across  the  terminals  of  the  condenser  which  results 
in  the  latter  becoming  "charged."  At  the  instant  of  reversal  of  polarity 
at  the  distant  station  the  condenser  discharges  through  the  extra  coil,  in  a 
direction  the  reverse  of  that  in  which  the  operating  current  in  the  main-  or 
artificial-line  coils  had  been  flowing.  The  result,  therefore,  is  that  the 
"turn-over"  of  magnetism  in  the  cores  of  the  relay  magnets  is  hastened 
considerably,  and  the  period  of  no-magnetism  correspondingly  shortened. 


THE  QUADRUPLEX  313 

The  insertion  of  the  4oo-ohm  coils  at  both  ends  of  the  line  naturally 
increases  the  total  resistance  of  the  circuit  800  ohms,  which  is  an  undesirable 
thing  to  do,  as  the  increased  resistance  reduces  the  efficiency  possible  where 
these  400-ohm  resistances  are  not  inserted  in  the  line.  One  method  of  elim- 
inating the  objectionable  additional  resistance,  which  permits  of  retaining 
the  efficacious  features  of  the  Smith  arrangement  is  that  of  transposing  the 
positions  of  the  polar  and  the  neutral  relays,  for  the  purpose  of  utilizing  the 
resistance  of  the  coil  windings  of  the  former  in  place  of  the  4oo-ohm  resistance 
coils  usually  connected  at  the  divide. 

Figure  270  shows  a  view  of  the  Smith  Neutral  Relay,  in  which  it  may  be 
seen  that  this  instrument  is  identical  in  construction  and  design,  with  the 


FIG.  270. — Neutral  relay  with  extra  binding  posts  to  which  are  attached  the  terminals  of 

the  extra  windings. 

ordinary  form  of  neutral  relay,  with  the  exception  that  two  additional 
binding-posts  are  provided  for  the  terminals  of  the  extra  coil,  which  consists 
simply  of  a  third  winding  over  the  cores  of  the  magnets  carrying  the  main- 
line and  artificial-line  windings. 

The  Diehl  "Bug-trap." — Another  very  effectual  method  of  tiding  over 
the  period  of  reversal  is  that  whereby  a  "bug-trap"  relay  (BT,  Fig.  271) 
in  connection  with  the  back-stop  of  the  neutral  relay,  is  used  to  introduce 
a  time  element  during  which  the  armatures  of  the  neutral  relay  and  the 
bug-trap  relay  must  traverse  the  gap  separating  their  back-  and  front-stops 
before  a  signal  will  be  registered  on  the  reading  sounder. 

A  glance  at  the  diagram  will  show  that  while  the  armature  of  the  neutral 
relay  may  flutter  uncertainly  against  its  front-stop  during  reversal  of  the 
long-end  battery  at  the  distant  end  of  the  line,  the  armature  of  the  reading 
sounder  will  remain  undisturbed  and  in  the  marking  position  until  the 
armature  tongue  of  the  relay  has  fallen  into  contact  with  its  back-stop. 

The  Diehl  bug-trap  is  extensively  employed  in  the  quadruplex  service 
of  the  Postal  Telegraph- Cable  Company. 


314 


AMERICAN  TELEGRAPH  PRACTICE 


The  Differential  "Bug-trap." — Figure  272  shows  a  "bug-trap"  arrange- 
ment employing  a  differentially  wound  bug-trap  relay  which  in  a  somewhat 
different  manner  accomplishes  the  same  purpose  as  the  Diehl  bug-trap  relay, 
and  the  repeating-sounder  arrangement  previously  described. 

Bug-trap  Suitable  for  Use  on 
Neutral  Side  of  "Decrement" 
Quad. — While  general  practice  pro- 
vides for  the  operation  of  the  neu- 
tral side  relays  by  an  " increment" 
of  current,  there  may  be  special  cases 
where  it  is  advisable  to  keep  the  long- 
end  battery  to  line  normally,  and  to 
operate  the  distant  neutral  relay  by  a 
"  decrement "  of  current. 

To  make  this  possible  the  only 
circuit  change  necessary  at  the  send- 
ing end  is  to  transpose  the  neutral 
side  transmitter  connections  so  that 
the  closed  key  will  cause  the  lower  potential  to  be  placed  to  line  and  the 
open  key  the  higher  potential. 

When  a  quadruplex  is  so  arranged  that  the  operation  of  the  neutral 
relays  is  the  result  of  a  decrement  of  current  strength,  it  follows  that  the 
reading  sounder  must  " close"  when  the  armature  tongue  of  the  line  relay 
makes  contact  with  its  back- 
stop instead  of  with  its  front- 
stop  as  with  the  more  com- 
mon arrangement. 

Figure  273  depicts  a 
differential  bug-trap  ar- 
rangement which  provides 
that  the  armature  of  the 
reading  sounder  will  be  in 
the  marking  position  while 


FIG.  271. — The  Diehl  bug- trap. 


FIG.  272. — Differential  bug- trap  relay. 


the  armature  tongue  of  the  neutral  relay  is  in  contact  with  its  back-stop, 
and  in  the  non-marking,  or  "spacing"  position  while  the  relay  armature  is 
not  in  contact  with  its  front-stop. 

The  "Condenser"  Bug-trap. — A  neutral-side  reading  sounder  arrange- 
ment used  in  British  Post  Office  telegraph  practice  which  has  been  found  to 
give  excellent  results,  is  illustrated  schematically  in  Fig.  274.  The  reading 
sounder  S,  has  a  resistance  of  1,000  ohms,  but  as  there  is  a  9,ooo-ohm  shunt 
around  the  coils  of  the  sounder  the  actual  or  joint-resistance  of  that  portion 
of  the  circuit  is  900  ohms. 

The  5o-ohm  coil  is  placed  in  the  circuit  for  the  purpose  of  curbing  the 


THE  QUADRUPLEX 


315 


sparking  that  would  appear  at  the  contact  points  of  the  relay  due  to  the 
discharge  from  the  condenser  when  the  circuit  is  completed.  The  capacity 
of  the  condenser  may  be  varied  from  2  to  8  m.f.  according  to  the  require- 
ments of  the  line  wire  operated,  while  the  resistance  in  series  with  the 
sounder  may  be  varied  from  100  to  700  ohms  in  steps  of  100  ohms.  The 
purpose  of  the  variable  resistance  is  to  "time"  the  discharge  from  the  con- 
denser and  the  discharge  due  to  inductance  in  the  coils  of  the  sounder,  thus 
making  it  possible  to  prolong  the  magnetization  of  the  cores  of  the  sounder 
magnets  over  the  period  required  to  maintain  the  armature  of  the  reading 
sounder  in  the  marking  position  while  the  armature  of  the  relay  momentarily 
breaks  circuit  during  the  periods  of  reversal  at  the  distant  station. 


2to8mf. 


BT 


; 


FIG.  2  73 . — Differential  bug-trap  arrange- 
ment for  use  on  neutral  side  of  "decrement" 
quadruplex. 


FIG.  274. — Condenser  bug- trap. 


If  the  circuits  shown  in  the  diagram  are  carefully  traced  it  will  be  seen 
that  while  the  armature  of  the  relay  is  in  the  closed  position  the  condenser 
takes  a  charge  due  to  the  difference  of  potential  which  exists  across  the  termi- 
nals of  the  sounder.  Now,  if  while  the  relay  tongue  is  in  contact  with  its 
front-stop  the  polarity  to  line  at  the  distant  station  is  reversed,  there 
will  be  a  momentary  break  in  the  sounder  circuit  controlled  by  the 
armature  of  the  neutral  relay.  At  the  instant,  however,  that  this  occurs 
the  condenser  discharges  through  the  only  circuit  presented  to  it — through 
the  sounder.  The  discharge  from  the  condenser  and  the  discharge  due  to 
the  inductance  of  the  sounder  magnets  results  in  prolonging  the  magnetiza- 
tion of  the  cores  of  the  sounder  until  current  from  the  opposite  battery  pole 
at  the  distant  end  of  the  line  has  had  time  once  more  to  resume  control  of 
the  armature  of  the  neutral  relay. 

THE  FREER  SELF-POLARIZING  NEUTRAL  RELAY 

Of  the  various  attempts  that  have  been  made  from  time  to  time,  to 
develop  a  type  of  relay  for  the  "second"  side  of  the  quadruplex,  which  would 
meet  the  requirements  more  satisfactorily  than  the  ordinary  types  of  neutral 


316 


AMERICAN  TELEGRAPH  PRACTICE 


relay;  the  product  which  has  survived  longest  is  that  known  as  the  Frier 
relay,  the  theoretical  arrangement  of  which  is  illustrated  in  Fig.  275. 

The  moving  element — the  armature — of  this  relay  is  pivoted  in  a  socket 
formed  in  the  pole-piece  of  an  extra  electromagnet  which  is  wound  differen- 
tially and  connected  into  the  main  line,  and  artificial  line  circuits  in  the  same 
manner  as  the  regular  line  coils  C  and  C\. 

A  current  in  the  extra  coil  Cz  will  result  in  the  core  of  that  magnet  having 
north  polarity  at  one  end  and  south  polarity  at  the  other  end.  Now  if 
the  end  of  the  core  upon  which  the  armature  (Fig.  275)  stands,  is  at  a  par- 
ticular instant  a  north  pole,  the  armature  extending  upward  between  the 
pole-faces  of  the  two  regular  magnets  will  be  magnetized  inductively  and 
have  a  north  polarity,  and,  as  obviously  the  windings  of  the  two  regular 
coils  are  so  connected  that  when  current  flows  in  the  circuit  made  up  through 

them,  the  pole-pieces  facing  the  arma- 
ture will  at  all  times  have  opposite 
polarities;  it  is  evident  that  the  polar- 
ized armature  will  move  toward  the 
pole-piece  which  at  that  instant  is  a 
south  pole. 

The  office  of  the  extra  coil  is  to 
maintain  the  polarity  of  the  armature 
at  all  times  in  opposition  to  the  coil  Ci 


Local 


FIG.  275. — Theory  of  the  Frier  neutral 
relay. 


regardless  of  the  direction  of  the  current 
flowing  in  the  circuit. 

In  Fig.  275  the  magnet  on  the  left  is  shown  as  presenting  a  north  pole, 
while  the  magnet  on  the  right  presents  a  south  pole  to  the  armature,  and  as 
the  latter  possesses  north  polarity  the  result  is  that  it  has  been  repelled 
from  the  left-hand  magnet  and  attracted  by  the  right-hand  magnet.  Should 
the  line  current  at  the  distant  station  be  reversed  while  the  armature  of  the 
relay  is  in  the  position  shown,  the  right-hand  magnet  will  present  a  north 
pole  to  the  armature;  but  as  at  the  instant  the  magnetism  in  the  right-hand 
magnet  is  reversed,  the  magnetism  of  the  core  of  the  extra  coil  also  is  reversed 
(and  consequently,  also  the  polarity  of  the  armature)  the  armature  remains 
in  connection  with  the  closed-contact  as  long  as  the  long-end  battery  at 
the  distant  station  is  to  line. 

The  method  by  which  the  armature  of  the  relay  is  made  immune  to 
short-end  reversals  from  the  distant  station,  is  the  same  as  that  employed 
in  the  operation  of  the  ordinary  neutral  relay;  namely  by  attaching  a  retract- 
ile spring  to  the  armature,  and  giving  it  a  tension  sufficient  to  hold  it  away 
from  the  closed-contact  when  the  short-end  only  is  to  line. 

Adjustment  of  the  Freir  Relay. — Under  ordinary  line  conditions,  the 
best  adjustment  to  give  the  armature  of  the  Freir  relay  is  such  that  the  gap 
between  the  armature  and  the  left-hand  magnet  will  be  about  twice  as 


THE  QUADRUPLEX   '  317 

wide  as  that  separating  the  armature  from  the  pole-face  of  the  right-hand 
magnet. 

OTHER  METHODS  OF  TIDING  OVER  THE  PERIODS  OF  REVERSAL 

From  what  has  hereinbefore  been  stated  in  regard  to  the  necessity  of 
establishing  a  time  interval  during  which  the  armature  of  the  second-side 
relay  may  be  made  to  ignore,  as  it  were,  the  period  of  " no-current"  which 
exists  while  the  long-end  current  at  the  distant  end  of  the  line  is  reversed, 
it  would  seem  of  the  utmost  importance  that  the  "reversal"  should  be  made 
with  the  greatest  possible  speed,  and  that  anything  which  can  be  done  to 
hasten  the  movement  of  the  armature  of  the  pole-changer  between  back- 
and  front-stops  during  operation,  will  have  a  directly  beneficial  effect  upon 
the  operation  of  the  distant  neutral  relay,  since  reducing  the  period  of  no- 
current  correspondingly  minimizes  the  task  set  for  the  bug-trap  arrangement- 
employed  in  any  given  system. 

It  might  here  be  restated,  as  covered  more  fully  elsewhere  herein,  that 
close  adjustment  of  the  points  of  the  pole-changer  between  which  the  arma- 
ture tongue  plays,  will  accomplish  more  in  the  way  of  reducing  the  interval 
of  no-current,  than  anything  else  that  may  be  contributed.  The  best  prac- 
tice in  this  regard  is  that  wherein  the  adjustment  of  pole-changer  and  trans- 
mitter points  brings  the  opposite  contact-points  as  close  together  as  sparking 
will  permit. 

THE  SHORT-CORE  OF  THE  NEUTRAL  RELAY 

In  the  design  of  nearly  all  forms  of  neutral  relays,  advantage  has  been 
taken  of  the  fact  that  by  reducing  the  length  of  the  iron  core  the  magnetism 
builds  up  to  its  full  strength  more  rapidly  than  where  comparatively  long 
cores  are  employed  in  winding  electromagnets. 

NEUTRAL  RELAYS  WITH  HOLDING  COILS 

When  the  Jones  quad  was  the  standard  of  the  Postal  Telegraph-Cable 
Company,  prior  to  the  adoption  of  the  Field  key  system,  the  neutral  relay 
was  equipped  with  a  third  coil  which  at  the  instant  of  " reversal"  was  charged 
by  means  of  a  form  of  induction  coil  known  as  the  inductorium. 

THE  INDUCTORIUM 

The  inductorium  consisted  of  an  iron  core  upon  which  three  coils  were 
wound,  one  coil  connected  in  series  with  the  main  line  coils  of  the  two  line 
relays,  another  in  series  with  the  artificial  line  coils  of  the  relays,  while  the  third 


318  AMERICAN  TELEGRAPH  PRACTICE 

coil  had  its  terminals  connected  directly  to  the  winding  of  the  third  coil  of 
the  neutral  relay;  the  latter  when  energized  serving  to  hold  the  armature  of 
the  relay  in  the  closed  position  for  a  brief  instant,  or  during  the  reversal  of 
the  distant  line-battery. 

Reversal  of  the  battery  at  the  distant  station  resulted  in  an  induced 
current  being  set  up  in  the  third  coil  (the  secondary  winding)  of  the  inductor- 
ium,  which  in  turn  energized  the  " holding-coil"  of  the  neutral  relay  at  the 
critical  moment,  thereby  tending  to  hold  the  armature  of  the  relay  in  contact 
with  its  front-stop  during  the  moment  of  no-magnetism  in  the  line  coils  of 
the  relay. 

HOLDING  COIL  OF  THE  NEUTRAL  RELAY  EMPLOYED  IN  THE  PRESENT 
WESTERN  UNION  QUADRUPLEX 

The  quadruplex  which  at  the  present  time  is  the  standard  in  the  service 
of  the  Western  Union  Telegraph  Company,  includes  a  form  of  neutral  relay 
which  is  equipped  with  a  holding  coil,  somewhat  similar  in  action  to  the  in- 
ductorium.  The  coil  is  placed  in  series  with  a  condenser  and  is  connected 
across  the  main  and  artificial  lines,  being  energized  at  the  instant  the  distant 
pole-changer  "breaks"  contact  with  either  battery  pole. 

The  effect  of  this  holding  coil  upon  the  efficiency  of  the  second  side  of  the 
Western  Union  quadruplex,  will  be  described  more  in  detail,  when,  presently, 
the  principles  of  that  quadruplex  are  explained. 

THE  WESTERN  UNION  QUADRUPLEX 

Figure  276  shows  a  theoretical  diagram  of  the  quadruplex  recently  a- 
dopted  as  standard  by  the  Western  Union  Telegraph  Company. 

The  improvements  incorporated  in  this  system  include  a  form  of  pole- 
changer  invented  by  Mr.  S.  D.  Field  and  illustrated  in  skeleton  in  Fig.  277. 

Like  the  pole-changer  used  in  connection  with  the  Postal  Telegraph- 
Cable  Co.'s  quadruplex,  this  instrument  may  be  used  also  as  a  "  transmitter  " 
on  the  second  side  of  the  quad.  The  magnet  on  the  left  of  the  armature  has 
a  solid  iron  core,  while  the  magnet  on  the  right  has  a  laminated  iron  core  and 
is  somewhat  shorter  than  the  former.  Each  magnet  is  wound  to  a  resistance 
of  4  ohms,  making  a  total  of  8  ohms  for  both  magnets  in  series,  and  the  re- 
spective coils  are  so  wound  that  the  magnetism  developed  in  each  pair  of 
coils  when  the  transmitting  key  is  depressed,  is  of  such  polarity  that  the  ac- 
tion of  one  magnet  opposes  that  of  the  other.  The  armature  is  situated 
between  the  opposing  pole-faces  of  the  electromagnets  and  has  attached  to 
it  a  retractile  spring  which  holds  the  armature  normally  toward  the  left-band 
magnet. 

When  the  transmitting  key  which  controls  the  operation  of  the  pole- 
changer  is  depressed,  both  magnets  are  energized,  but  the  magnetism  builds  up 


THE  QUADRUPLEX 


319 


cr 

T3 

3 

T3 

d 


320 


AMERICAN  TELEGRAPH  PRACTICE 


much  more  rapidly  in  the  right-hand  magnet  than  in  the  other,  due  to  the  fact 
that  the  former  is  considerably  shorter  and  that  it  has  a  laminated  iron  core, 
and  to  the  further  fact  that  in  practice  the  coils  of  the  longer  magnet  are 
shunted  with  a  resistance  coil,  the  total  result  of  which  is  that  the  left-hand 
magnet  does  not  acquire  its  maximum  magnetic  strength  until  the  armature 
has  been  drawn  into  contact  with  the  main-line  battery  contact  on  the  right; 
remaining  there  until  the  signaling  key  is  released  or  opened. 


-o 


— P 


•8 Ohms- 


FIG.  277. — Form  -|of  pole-changer  and  transmitter  used  in  connection  with  the  W.  U. 

quadruplex. 

At  the  instant  the  signaling  key  is  released — thus  opening  the  battery 
circuit  through  the  coils  6f  the  pole-changer — the  laminated  core  of  the  right- 
hand  magnet  instantaneously  loses  its  magnetism,  permitting  the  retractile 
spring  aided  by  the  slowly  disappearing  magnetism  in  the  long  core,  to  rapidly 
draw  the  armature  into  contact  with  the  opposite  battery  contact. 

The  object  aimed  at  is  to  hasten  the  transit  of  the  armature,  thereby 
reducing  to  a  corresponding  degree  the  interval  during  which  the  main-line 
battery  is  not  applied  to  the  line. 

THE  W.  U.,  NEUTRAL  RELAY 

Figure  278  shows  in  skeleton  the  usual  differential  windings  of  the  main- 
line and  artificial-line  circuits,  each  wound  to  a  resistance  of  350  ohms,  while 
situated  immediately  above  the  line  magnet  is  shown  a  "holding"  magnet. 
It  is  evident  from  the  circuit  arrangements  illustrated  in  Fig.  276  that 
this  quadruplex  embodies  principles  common  to  the  "bridge"  and  to  the 
" differential"  multiplex  systems,  inasmuch  as  the  polar  relay  occupies  a 
position  the  same  as  that  occupied  by  the  relay  used  in  the  bridge  duplex, 
while  the  neutral  relay  has  one  of  its  windings  connected  in  series  with  the 
main-line  wire,  and  the  other  in  series  with  the  artificial-line  circuit. 


THE  QUADRUPLEX 


321 


The  Holding  Coil. — As  shown  at  H,  Fig.  276,  the  holding  coil  is  con- 
nected across  the  main  and  artificial  lines  in  series  with  a  condenser  HC 
which  accumulates  a  charge  while  battery  is  applied  to  the  line  at  the 
distant  station.  As  the  distant  pole-changer  armature  leaves  either  battery 
contact,  the  home  condenser  almost  immediately  thereafter  discharges 
through  the  path  provided  for  it — through  the  holding  coil — thus  tending  to 
hold  the  armature  of  the  neutral  relay  in  the  closed  position  during  a  period 
which  approximates  in  duration  that  required  by  the  armature  of  the  distant 
pole-changer  to  travel  from  one  battery  contact  to  the  other. 


FIG.  278. — Neutral  relay  used  in  connection  with  the  W.  U.  quadruplex. 

The  Impedance  Coil. — In  the  bridge  duplex,  Fig.  233,  page  268,  the 
four  arms  of  the  bridge  consist  of  the  line  wire,  the  artificial  line,  the  arm 
rf,  and  the  arm  r.  The  latter  two  resistances  have  identical  values.  In 
British  Post-office  telegraph  practice  each  arm  is  given  a  value  of  3,000 
ohms. 

In  the  quadruplex  -under  consideration  the  corresponding  arms  are 
represented  by  the  two  windings  of  an  impedance  or  retardation  coil  ($U, 
Fig.  276)  which  has  a  circular  core  built  up  of  iron  wires  forming  a  closed 
magnetic  circuit.  The  windings  are  differential,  each  coil  having  a  resistance 
of  500  ohms. 

In  the  bridge  duplex,  employing  non-inductive  resistance  units  to  form 
the  two  "bridge"  arms,  the  operation  of  the  polar  relay  is  dependent  upon 
the  existing  difference  of  potential  across  the  terminals  of  the  relay,  which 
necessitates  that  in  order  to  have  an  operating  current  of  sufficient  value 
to  insure  quick  responce  of  the  relay  armature,  the  resistance  of  the  "arms" 
of  the  bridge  must  be  high  enough  to  maintain  the  required  difference  of 
potential. 

When  the  non-inductive  bridge  arms  are  replaced  by  arms  possessing  a 

considerable  amount  of  retardation  or  impedance,  the  operation  of  the  polar 
21 


322 


AMERICAN  TELEGRAPH  PRACTICE 


relay  is  not  dependent  solely  upon  the  difference  of  potential  existing  across 
its  terminals,  as,  in  this  case  (see  Fig.  276)  the  received  current  finds  a  less 
obstructed  path  through  the  relay  than  through  the  upper  arm  of  the  bridge 
coil,  because  the  latter  presents  " impedance"  which  "retards"  the  flow  of 
current  into  it:  at  least,  the  first  part  of  each  received  current  wave  is 
diverted  through  the  relay,  causing  it  to  actuate  its  armature  without  having 
to  wait  for  the  current  due  to  difference  of  potential  across  the  bridge  arms. 

The  Ohm's  law  current,  of  course,  builds 
up  gradually  as  the  magnetic  inertia  of  the 
retardation  coil  is  overcome,  and,  if  the  cir- 
cuit is  properly  timed,  in  this  regard;  comes 
along  in  time  to  hold  the  armature  of  the 
relay  in  the  desired  position. 

In  view  of  the  fact  that  the  first  part  of 
the  received  impulse  is  diverted  through  the 
relay  circuit  it  is  not  necessary  (on  account 
of  the  inductance  possessed  by  the  alterna- 
tive path)  to  have  high  ohmic  resistance  in 
the  bridge  arms. 

In  the  Western  Union  arrangement,  there- 


FIG.  279. — 5-U  impedance  coil. 


fore,  each  coil  has  a  resistance  of  500  ohms  instead  of  the  3,000  ohms  per 
arm  used  in  the  old  form  of  bridge  duplex.  Indeed,  it  has  been  found  prac- 
ticable in  ocean  cable  duplex  operation  to  employ,  bridge  arms  having  a 
resistance  of  1 5  ohms  each,  but  in  this  case  the  coils  are  of  large  dimensions 
and  have  an  inductance  of  15  henries  each.1 


EFFECT  OF  THE  $-U  COIL  UPON  OUT -GOING  CURRENTS 

The  fact  that  the  windings  of  the  coil  are  differential,  and  that  the  action 
of  one  coil  neutralizes  the  action  of  the  other;  so  far  as  the  magnetic  effects 
produced  in  the  iron  are  concerned,  provides  that  to  out-going  currents  there 
will  be  no  appreciable  retardation. 

It  is  obvious  that  with  equal  current  strengths  in  each  coil  of  the  bridge, 
no  magnetism  is  produced  in  the  core.  This  being  the  case  the  situation 
is  the  same  as  if  no  iron  core  were  inserted  within  the  coils;  or,  as  if  the  coils 
were  simple  solenoids. 

We  are  dealing  with  the  characteristics  of  the  magnetic  field  set  up  in  the 
space  immediately  surrounding  the  coil  windings,  and  inasmuch  as  there  is  no 
magnetism  in  the  core,  the  " extra  current"  due  to  self-induction  will  be  of 
low  value  in  comparison  with  that  which  would  be  produced  due  to  the 
stronger  magnetic  field  were  the  core  magnetized.  Consequently,  as  the 

1  The  "bridge-resistance"  used  in  ocean  cable  work  is  known  as  the  Brown  magnetic 
bridge,  being  the  invention  of  Mr.  S.  G.  Brown. 


THE  QUADRUPLEX  323 

impedance  presented  to  the  out-going  impulses,  would  consist  mainly  of  the 
reverse,  or  opposing  currents  due  to  self-induction  of  the  coil,  it  is  at  once 
apparent  that  the  impedance  will  be  less  when  the  core  is  not  magnetized. 

Naturally  there  will  be  a  certain  amount  of  "choke"  due  to  the  con- 
tiguous turns  of  the  winding  of  the  coil  in  either  arm,  but  this  is  small  in 
comparison  with  what  it  would  be  in  one  coil,  were  the  circuit  through  the 
companion  coil  opened;  or,  if  the  windings  were  not  differential. 

The  amount  of  retardation  natural  to  the  coil  winding  graduates  the  rise 
and  fall  of  the  out-going  currents,  and  this  in  connection  with  the  spark  con- 
denser (SC,  Fig.  276)  reduces  considerably  the  strength  of  the  electrostatic 
induction  which  otherwise  would  take  place  between  the  line  wire  and 
neighboring  conductors  on  the  same  pole  line,  or  in  the  same  cable. 

THE  EFFECT  OF  THE  5-U  COIL  UPON  THE  HOME  RELAYS 

It  is  needful  now  to  look  to  the  effects  produced  in  the  home  receiving 
relays  due  to  the  action  of  the  bridge  coil. 

Obviously,  the  only  time  when  there  is  no  magnetism  in  the  core  of  the 
bridge  coil  is  when  identical  current  values  obtain  in  both  main  and  arti- 
ficial lines.  The  operation  of  the  distant  pole-changer,  naturally,  causes 
magnetic  variations  in  the  core  of  the  retardation  coil  at  the  home  station, 
and  the  extra  currents  produced  as  a  result  thereof  traverse  the  coils  of  the 
polar  relay  in  a  direction  which  aids  the  incoming  currents  from  the  distant 
station  in  effecting  the  movement  of  the  armature  of  the  relay  in  the  desired 
direction.  Also,  under  certain  conditions  during  the  period  of  reversal  at 
the  distant  station,  the  instant  the  armature  of  the  pole-changer  leaves 
either  battery  contact,  magnetic  variations  in  the  home  bridge  coil  produce 
extra  currents,  which,  having  a  path  across  the  main  line  and  artificial  line 
by  way  of  the  holding  coil  of  the  neutral  relay,  aid  the  discharge  current 
from  the  condenser  HC  in  holding  the  tongue  of  the  neutral  relay  in  contact 
with  its  front-stop  during  the  critical  period. 

OPERATION  OF  THE  W.  U.  QUAD 

By  referring  to  Fig.  276,  it  will  be  seen  that  the  line  currents  are  furnished 
by  two  dynamos,  the  negative  pole  of  one  machine  being  connected  to  the 
" closed"  contact  of  the  pole-changer,  while  the  positive  pole  of  the  other 
dynamo  is  connected  to  the  "open"  contact  of  the  pole-changer;  the  opposite 
pole  of  each  dynamo  being  grounded. 

The  ratio  of  long-end  to  short-end  current  is  3  to  i,  and  the  method 
employed  to  obtain  the  desired  proportions  is  the  same  as  in  the  Field  quadru- 
plex.  In  Fig.  276,  the  added  resistance  is  shown  at  AR  and  the  leak 
resistance  at  LR. 


324  AMERICAN  TELEGRAPH  PRACTICE 

At  the  station  shown  on  the  left  the  pole-changer  PC  is  represented  as 
sending  a  positive  current  to  line,  the  strength  of  which  has  been  reduced 
to  the  short-end  value  on  account  of  having  a  joint-path;  on  the  one  hand 
via  the  added  resistance  AR,  to  ground  at  the  distant  station,  and  at  the  end 
of  the  artificial  line  at  the  home  station :  on  the  other  hand  from  the  pole- 
changer  armature  to  ground  at  the  home  station  via  the  leak  resistance 
LR.  None  of  the  out-going  current  will  pass  through  the  coils  of  the  polar 
relay  provided  the  resistance  of  the  artificial  line  has  been  adjusted  to  equal 
that  of  the  main-line  and  distant  apparatus  to  ground,  for  the  reason  that 
under  such  conditions  there  is  no  difference  of  potential  across  the  terminals 
of  the  relay.  The  same  is  true  of  the  holding  coil  H,  of  the  neutral  relay. 

In  the  case  of  the  neutral  relay  and  the  retardation  coil,  it  is  seen  that 
each  of  these  instruments  has  wound  upon  its  iron  core  one  coil  in  series 
with  the  main-line  wire,  and  one  coil  in  series  with  the  artificial  line  circuit. 
In  other  words  each  instrument  is  wound  differentially,  with  the  result 
that  when  equal  current  strengths  obtain  in  each  winding,  the  tendency  of 
one  coil  to  magnetize  the  core  is  nullified  by  the  action  of  the  companion 
coil. 

It  is  plain,  therefore,  that  under  well-balanced  conditions  the  home  relays 
are  unresponsive  to  out-going  signals. 

The  action  of  the  received  current  may  be  traced  by  assuming  that  a 
short-end  impulse  has  been  transmitted  from  the  station  on  the  left  to  the 
station  shown  on  the  right  (Fig.  276).  Obviously,  the  current  passes  through 
the  main-line  coil  of  the  neutral  relay  NR,  and  through  the  holding-coil  H  (in 
the  winding  of  the  latter  the  current  exists  only  while  the  condenser  HC  is 
taking  on  its  charge),  but  as  the  retractile  spring  attached  to  the  armature 
of  the  neutral  relay  has  previously  been  given  a  tension  which  holds  it  in 
contact  with  its  back-stop  until  the  long-end  potential  has  been  applied 
at  the  distant  end  of  the  line,  the  relay  is  unaffected.  After  passing  through 
the  line  coil  of  the  neutral  relay  the  received  impulse  finds  two  paths  open  to 
it;  one  through  the  polar  relay  PR,  and  one  through  the  coil  5  U.  In  attempt- 
ing to  enter  the  line  coil  of  the  latter,  the  current  upsets  the  magnetic  balance 
of  the  coil  by  magnetizing  the  core  (due  to  the  increased  current  volume  now 
flowing  in  one  winding  over  that  flowing  in  the  other)  with  the  result  that  the 
extra  current  of  self-induction  thereby  created,  opposes  the  flow  of  the  line 
current;  momentarily  at  least,  or  until  the  head  end  of  the  received  current 
wave  has  been  diverted  through  the  path  containing  the  polar  relay. 

As  the  armature  of  the  polar  relay  is  moved  into  the  closed  or  marking 
position,  the  current  builds  up  through  the  line  winding  of  the  impedance 
coil,  and  joins  that  portion  of  the  current  which  has  passed  through  the  polar 
relay  and  the  other  winding  of  the  impedance  coil,  passing  thence  to  ground 
via  the  transmitting  instruments  and  dynamo. 

Figure  280  shows  the  actual  instrument  binding-post  connections  of 


THE  QUADRUPLEX 


325 


Line 


Lightning 
Arrester 


FIG.  280. — Instrument  main  line  binding-post  connections  W.  U.  quadruplex. 


326 


AMERICAN  TELEGRAPH  PRACTICE 


the  Western  Union  quadruplex.  The  "Line  resistance  box"  shown  in  the 
upper  right  hand  corner  of  the  diagram  (an  enlarged  view  of  which  is  shown  in 
Fig.  281)  is  made  up  of  two  independent  variable  resistances,  of  1,250  ohms 
total  each,  equipped  with  a  common  double-lever  switch  for  the  purpose  of 
throwing  equal  amounts  of  resistance  into  the  main  line  and  into  the  arti- 
ficial line  simultaneously. 

One  use  to  which  this  resistance  is  put,  is  to  increase  the  resistance  of 
comparatively  short  lines  which  it  is  desired  to  operate  quadruplex  with 
the  regular  long-line  potentials.  Inserting  additional  resistance  in  both 
main  and  artificial  lines  adds  to  the  electrical  length  of  line  wires  which  in 


FIG.    281. — "Line"  resistance  box  W.  U.  quadruplex. 

themselves  would  be  so  low  in  resistance  that  the  currents  from  the  regular 
dynamos  would  be  excessive. 

The  insertion  of  added  resistance  in  the  line  immediately  in  front  of  the 
home  apparatus  is  of  considerable  benefit  in  caring  for  quick  changes  in  the 
insulation  of  the  line  wire  during  wet  weather,  for  the  reason  that  with  800 
or  1,000  ohms  of  the  external  circuit  perfectly  insulated  from  the  ground 
(as  would  be  the  case  when  that  much  added  resistance  is  inserted  in 
series  with  the  line)  the  insulation  of  the  entire  line,  per  electrical  mile, 
is  considerably  higher,  and  as  a  consequence  permits  of  greater  variation  in 
the  resistance  of  the  exposed  section  of  the  line,  without  seriously  affect- 
ing the  "balance."  It  is  necessary,  of  course,  when  such  additional  re- 
sistance has  been  inserted  in  the  line  at  one  end  of  a  quadruplexed  circuit, 
to  notify  the  distant  office  of  the  fact,  so  that  the  line  balance  at  the  distant 
end  may  be  changed  to  compensate  for  the  added  resistance. 


THE  QUADRUPLEX 
THE  MILAMMETER 


327 


The  milammeter  shown  in  the  diagram,  Fig.  280  (an  enlarged  view  of 
which  is  shown  in  Fig.  282)  is  connected  in  series  with  the  polar  relay  in  the 
bridge  circuit  for  the  purpose  of  facilitating  the  operation  of  balancing. 


FIG.  282. — Milammeter  used  in  "balancing"  duplexes  and  quadruplexes. 

tO 


FIG.  283.— W.  U.  artificial-line  rheostat. 


328 


AMERICAN  TELEGRAPH  PRACTICE 


THE  QUADRUPLEX 


329 


Figure  283  shows  the  binding-post  connections  of  the  artificial-line 
rheostat. 

Figure  284  is  a  diagram  of  the  connections  of  both  main-line  and  local 
circuits  of  the  W.U.  quadruplex/  The  spring-jacks  SJ  represent  the  loop- 
board  terminals  of  the  receiving  and  sending  " sides"  of  the  polar  and  com- 
mon sides  of  the  set. 


THE  BRITISH  POST-OFFICE  QUADRUPLEX 

The  quadruplex  system  used  in  British  Post-Office  telegraph  service,  is, 
in  theory,  practically  the  same  as  the  original  American  quadruplex  systems. 

A  theoretical  diagram  of  the  main-line  circuits  is  shown  in  Fig.  285,  a 
consideration  of  which  will  show  that  the  " increment  key"  IK  serves  the 
same  purpose  as  the  transmitter  employed  on  the  second  side  of  the  American 
systems;  namely  to  place  either  the  short-  or  the  long-end  battery  to  line, 
while  the  "reversing  key"  RK  serves  as  a  pole-changer. 


Line 


FIG.  285. 

In  the  diagram  submitted  herewith  the  transmitting  keys  are  shown  in 
American  conventional  outline,  for  the  purpose  of  clearly  portraying  the 
action  of  each  instrument.  The  actual  appearance  of  one  key  is  about 
the  same  as  that  of  the  other.  Both  are  larger  and  more  massive  than  the 
American  key,  and  the  contact  points — which  are  mounted  at  the  end  of 
the  key  remote  from  the  hard-rubber  knob — are  enclosed  in  a  dust-proof 
metal  cylinder  with  a  glass  top,  see  Fig.  2850. 

The  reversing  key,  or  A  key  as  it  is  termed  in  Great  Britain  has  its 
battery  contact  point  so  arranged  that  the  continuity  of  the  circuit  from 
the  battery  is  preserved  while  the  lever  passes  from  positive  to  negative 
battery  terminal  or  -vice  versa.  Obviously  a  momentary  short  circuit  exists 
during  the  reversal  of  current,  the  same  as  in  the  case  of  the  continuity  pre- 
serving transmitter  employed  in  connection  with  the  Stearns  duplex. 

The  increment,  or  B  key  is  so  constructed  that  the  battery  is  never  cut 
off  from  the  A  key.  In  order  that  this  may  be  satisfactorily  accomplished 


330  AMERICAN  TELEGRAPH  PRACTICE 

it  is  necessary  to  so  adjust  the  contact  points  that  the  lever  will  make  con- 
tact with  one  battery  terminal  before  breaking  with  the  other. 

For  the  purpose  of  curbing  the  sparking  at  contact  points  when  full 
potential  is  to  line  a  loo-ohm  resistance  coil  is  connected  as  shown  at  R} 
Fig.  285. 

It  is  necessary  that  the  resistance  of  the  battery  should  be  the  same 
regardless  of  the  position  of  the  keys  at  any  instant,  otherwise  the  balance 


FIG.  2850".— Transmitting  key,  B.  P.  O.  quadruplex. 

at  the  distant  station  would  be  disturbed  when  the  positions  of  the  keys 
are  altered.  It  is  necessary,  therefore,  to  insert  a  resistance  r  in  the  tap 
wire  equal  to  the  resistance  of  the  long-end  battery,  plus  the  loo-ohm  spark 
coil.  With  the  key  IK  in  the  position  shown  in  the  diagram  the  internal 
resistance;  including  that  of  the  short-end  battery,  is  the  same  as  that 
obtaining  when  the  key  is  depressed. 

The  type  of  polar  relay  used  is  that  known  as  the  Wheatstone  relay. 

The  differential  neutral  relay,  or  B  relay,  has  its  local  connections  arranged 
as  shown  in  Fig.  274. 


CHAPTER  XV 
"BALANCING"  DUPLEXES  AND  QUADRUPLEXES 

If  the  reader  will  review  that  part  of  Chapter  XIII,  dealing  with  "The 
Differential  Relay"  (Fig.  217),  and  "The  Artificial  Line "  (Fig.  218)  he  will 
recognize  the  necessity  for  a  correct  "ohmic"  and  "static"  balance  of  lines 
operated  duplex  or  quadruplex. 

In  describing  the  various  duplex  and  quadruplex  systems  in  the  preceding 
text  matter,  "methods"  of  balancing  each  system  have  been  purposely 
omitted,  for  the  reason  that  with  all  systems  the  requirements  are  the  same, 
and  that  the  author  during  a  fairly  extensive  teaching  experience  has  found 
that  no  little  confusion  exists  in  the  minds  of  students,  when  the  idea  pre- 
vails that  each  system — so-called — of  duplex  or  quadruplex  telegraphy  can 
be  balanced  only  by  some  particular  process  or  method. 

It  is  true  that  the  various  telegraph  administrations  furnish  "rules" 
for  the  guidance  of  employees  in  balancing  the  particular  duplex  and  quad- 
ruplex employed  in  each  case,  some  of  which  will  be  incorporated  herein ;  but 
it  should  be  borne  in  mind  that  the  procedure  in  every  instance  has  the  same 
purpose  in  view,  viz.,  that  of  establishing  an  "ohmic"  and  "static"  balance 
between  the  main-line  wire  and  the  artificial  line. 

THE  RESISTANCE,   OR  "OHMIC"  BALANCE 

In  Fig.  286,  the  artificial  line  rheostat  is  shown  as  having  a  resistance  of 
2,400  ohms.  Although  of  secondary  importance — so  far  as  the  balance  is 


Line 


FIG.  286. — Balancing  the  main  and  artificial  lines. 

concerned — it  is  well  to  learn  what  the  unplugged  resistance  of  the  rheostat 
represents. 

In  the  typical  case  presented  in  Fig.  286,  as  in  all  similar  installations, 
the  2,400  ohms  in  the  rheostat  at  station  A  represents  the  resistance  of  the 

331 


332  AMERICAN  TELEGRAPH  PRACTICE 

line  wire  beyond  the  home  relay,  the  resistance  of  the  main-line  coil  of  the 
relay  at  B,  plus  the  joint-resistance  of  the  artificial-line  circuit  to  ground 
(including  the  resistance  of  the  artificial-line  coil  of  the  relay)  and  the  circuit 
to  ground  via  the  battery  or  dynamo ;  or, 

600  X (200  +  2400) 

v  =487  ohms 
600 +  (200 +  2400) 

and 

487+200+1,713  =  2,400  ohms. 

The  indicated  resistance  of  the  artificial-line  rheostat  at  A,  therefore, 
represents  the  1,713  ohms  line  resistance,  plus  the  resistance  of  the  mairL-line 
coil  of  the  relay  at  B  (in  this  case  200  ohms)  plus  the  joint-resistance  of  the 
battery  circuit  and  the  artificial-line  circuit  from  the  point  X  at  B. 

The  reason  why  the  resistance  of  the 
relay  at  A  does  not  enter  into  the  calcu- 
lation is  that  the  resistance  of  one  side 
already  balances  the  resistance  of  the  other. 
If,  for  instance,  the  resistance  of  the  arti- 
ficial-line coil  were  regarded  as  a  part  of 

1         MMMf  ^e  tota^  resistance  °f  the  artificial  line, 

[       then  the  resistance  of  the  main-line  coil  of 
the  relay  would  have  to  be  regarded  as  a 

FIG.  287.— Principle  of  the  bridge  Part  of  the  total  line  resistance,  and  the  in- 
balance.  .dicated  resistance  of  the  rheostat  would  re- 

main the  same. 

That  this  is  true  may  readily  be  seen  by  considering  the  conditions  of 
current  obtaining  in  a  wheatstone  bridge  circuit,  see  Fig.  287. 

The  "bridge"  coils  a  and  b  occupy  the  same  positions  in  the  circuit  that 
the  AL  and  ML  coils  of  the  differential  relay  occupy  in  a  duplex  or  quadruplex 
circuit,  while  the  bridge  arm  R  represents  the  line  wire,  and  the  arm  X  the 
artificial  line  of  a  duplex  or  quadruplex  circuit.  The  galvanometer  G  is 
connected  across  the  terminals  of  the  coils  a  and  b  for  the  purpose  of  indicating 
the  presence  of  current  in  the  galvanometer  circuit. 

As  was  explained  in  describing  the  principle  of  the  Wheatstone  Bridge 
(Fig.  138)  no  current  will  flow  through  the  galvanometer  circuit  when  the 
resistance  of  a  equals  the  resistance  of  b  and  the  resistance  of  R  equals  the 
resistance  of  X.  Therefore,  if  in  the  duplex  or  quadruplex  circuit  the  resist- 
ance of  one  winding  of  the  relay  equals  the  resistance  of  the  other  winding, 
the  circuit  will  be  balanced  when  the  resistance  of  the  rheostat  is  adjusted  to 
equal  the  resistance  of  the  line  wire  to  ground  via  the  distant  apparatus. 

It  is  apparent  also,  that  the  resistance  of  the  rheostat  will  remain  the 
same  regardless  of  the  resistance  of  the  coils  of  the  home  relay,  provided  the 


CAPACITY,  OR  STATIC  BALANCE  333 

resistance  of  each  coil  is  the  same.  In  Fig.  286,  for  instance,  the  rheostat 
resistance  (2,400  ohms)  would  remain  the  same  and  the  home  balance  would 
be  unaffected  if  the  resistance  of  the  home  relay  were  changed  to,  say,  20 
ohms  instead  of  200  ohms  per  winding. 

The  resistance  balance  may  be  established  by  adjusting  the  resistance  of 
the  artificial-line  rheostat  until  the  armature  of  the  differentially  connected 
polar  relay,  neutral  relay,  or  galvanometer  remains  passive  to  the  operation 
of  the  home  pole-changer  while  the  line  is  grounded  at  the  distant  station, 
and  in  the  case  of  a  "bridged"  polar  relay  or  galvanometer;  until  the  armature 
and  pointer,  respectively,  of  those  instruments  indicate  "no  current." 

THE  CAPACITY,  OR  "STATIC"  BALANCE 

As  pointed  out  elsewhere  herein,  when  battery  is  applied  to  a  line  the 
conductor  has  to  be  "charged"  before  the  recording  instrument  at  the  distant 
end  of  the  line  will  indicate  the  presence  of  current  in  its  coil  windings. 

When  the  key  K  is  closed  (Fig.  286)  a  rush  of  current  takes  place  into 
the  circuit  which  possesses  capacity — the  line  wire — passing  through  •  the 
main-line  coil  of  the  relay,  magnetizing  its  core  momentarily,  thereby  pro- 
ducing a  kick  of  the  armature  which  seriously  interferes  with  intended 
signals.  Also,  upon  opening  the  key  the  line  "discharges,"  again,  momenta- 
rily energizing  the  main-line  winding  of  the  relay,  thereby  producing  a  false 
signal. 

Line 


<Q  Relay 

-5L 


The  above  described  action  takes  place  when  the  circuit  has  been  given 
an  "ohmic"  balance,  only.  When,  however,  the  artificial  line  has  been 
provided  with  artificial  capacity  in  the  form  of  an  adjustable  electric  con- 
denser connected  across  the  terminals  of  the  rheostat  as  shown  in  Fig.  288, 
a  "capacity"  balance  may  be  established,  so  that  the  charges  and  discharges 
in  the  artificial -line  circuit  will  at  all  times  equal  those  in  the  main  line. 

When  battery  is  applied  to  a  line  wire  the  distant  end  of  which  is  "open, " 
or  insulated  from  the  earth,  the  value  of  the  charge  may  be  represented  as 
in  Fig.  289.  In  the  illustration  the  negative  pole  of  the  dynamo  is  "  earthed  " 


334 


AMERICAN  TELEGRAPH  PRACTICE 


or  grounded,  while  the  positive  pole  is  applied  to  the  line,  giving  the  line  a 
positive  charge. 

If  after  the  wire  has  been  charged,  the  lever  of  the  switch  S  is  moved  into 
contact  with  the  ground  connection  G,  the  charge  will  flow  out  of  the  line  to 
ground. 


Positive  Charge 


FIG.  289. 


Negative  Charge 


FIG.  290. 


The  assumed  rectangular  shape  of  the  charge  in  this  case  is  due  to  the 
fact  that  the  same  difference  of  potential  exists  throughout  the  entire 
length  of  the  line. 

The  charge  held  by  a  line  wire  which  is  grounded  at  the  distant  end  may 
be  represented  as  in  Fig.  290,  and  as  in  this  case  the  negative  pole  of  the 
dynamo  is  applied  to  the  line,  giving  the  latter  a  negative  charge;  the  shaded 
area  is  shown  below  the  line. 

It  will  be  seen  that  the  value  of  the 
charge  along  the  conductor  " drops" 
with  the  potential.  In  other  words,  the 
value  of  the  charge  is  greatest  at  the 
battery  end  of  the  line;  the  value  de- 
creasing directly  with  decrease  of  the 
difference  of  potential  along  the  con- 
ductor; between  the  line  and  the  earth, 
until  finally  when  the  zero  potential  of 
the  earth  obtains,  the  charge  has  zero 


FIG.  291. 


value.  It  may  be  noted  that  the  amount  of  charge  held  by  the  conductor— 
as  represented  by  the  area  of  the  shaded  section — in  the  case  of  the  open 
wire,  is  twice  as  great  as  that  held  by  the  grounded  wire,  assuming,  of  course, 
that  the  value  of  the  applied  e.m.f.  is  identical  in  each  instance. 

When  battery  is  applied  at  both  ends  of  a  line,  positive  at  one  end  and 
negative  at  the  other,  the  two  charges  held  will  be  distributed  as  illustrated  in 
Fig.  291.  In  this  case  there  is  a  fall  of  potential  from  each  end  of  the  circuit 
toward  the  center,  and,  as  at  the  electrical  center  of  the  line  the  potential  will 
have  zero  value,  the  charge  at  that  point  will  be  nil.1 

1  In  practice  the  electrical  center  may  be  far  from  the  geographical  center  of  the  line. 
A  circuit,  for  instance,  may  include  a  comparatively  small  coil  of  wire  which  has  a  resistance 
equal  to  many  miles  of  line  wire,  and  as  the  potential  falls  directly  as  resistance  is  overcome, 


TIMING  THE  CONDENSER  DISCHARGE  335 

It  will  be  seen  that  if  the  switch  5  (Fig.  291)  were  opened,  the  charge  upon 
the  line  would  take  the  form  illustrated  in  Fig.  289,  and  it  is  evident  that  in 
the  operation  of  duplex  and  quadruplex  circuits  all  of  these  conditions  of 
charge  will  obtain  at  different  times  during  actual  operation,  and  that  the 
office  of  the  condenser  associated  with  the  artificial-line  at  each  end  of  the 
main-line  is  to  produce  in  the  artificial  circuit,  effects  identical  with  those 
occurring  in  the  main  line  at  any  given  instant. 

As  before  stated  the  terminals  of  the  rheostat  are  shunted  by  a  condenser 
(or  pair  of  condensers  connected  in  parallel)  of  such  capacity  that  the  charge 
and  discharge  effects  in  the  artificial-line  circuit  may  be  made  to  equal  the 
charges  and  discharges  taking  place  in  the  main-line  circuit.  The  effect  of  the 
charge  passing  into  the  line  wire  through  the  relay  coils  is  to  produce  a  for- 
ward, or  "marking"  kick  of  the  relay  armature,  while  the  effect  of  the  charge 
passing  into  the  condenser  circuit  at  the  same  instant  is  to  produce  a  backward 
or  "spacing"  kick  of  the  armature,  hence  when  the  capacity  of  the  condenser 
is  correctly  adjusted  the  disturbing  effects  are  counterbalanced,  and  the  line  is 
said  to  have  been  given  a  capacity  balance. 

TIMING  THE  CONDENSER  DISCHARGE 

As  the  time  required  to  charge  a  line  is  longer  the  greater  the  length  of  the 
line,  it  follows  that  the  time  required  for  the  line  to  discharge,  also  varies 
according  to  the  length  of  the  line.  In  order  to  introduce  the  element  of 
"time"  into  the  condenser  circuit  also,  it  is  the  usual  practice  to  place  an  ad- 
justable resistance  in  series  with  each  of  the  two  condensers  associated  with 
the  artificial  line,  as  shown  in  Fig.  219. 

The  discharge  of  the  condenser  produces  a  current  the  duration  and 
quantity  of  which  is  dependent  upon  the  electrical  properties  of  the  circuit 
through  which  it  is  made  to  discharge. 

In  accordance  with  Ohm's  law  a  condenser  requires  twice  as  long  to  dis- 
charge itself  through  a  resistance  of  600  ohms  as  through  a  resistance  of  300 
ohms.  In  order  that  the  discharge  of  the  condensers  in  the  artificial  line  shall 
balance  the  discharge  from  the  line  conductor,  it  is  necessary  that  the  currents 
be  of  the  same  duration  as  well  as  of  the  same  quantity.  In  other  words,  on 
each  occasion  when  the  two  discharges  take  place  they  must  have  an  exactly 
equal  value  and  effect. 


the  ohmic  center  of  the  circuit  may  be  but  a  hundred  miles  distant  from  one  terminal  of  a 
Soo-mile  line.  The  same  would  be  true  of  a  circuit  made  up  partly  of  copper  wire  and  partly 
of  iron  wire,  owing  to  the  fact  that  in  a  given  amount  of  resistance  there  would  be  a  greater 
number  of  miles  of  copper  wire  than  of  iron  wire  of  like  gage.  Also  it  will  be  found  that 
where  any  considerable  length  of  line  conductor  passes  through  a  cable,  that  portion  of 
the  conductor  may  have  a  capacity  equal  to  that  of  a  much  greater  length  of  open-line  wire. 
These  are  the  factors  responsible  for  the  discrepancies  often  noted  in  the  amount  of 
artificial  capacity  required  at  each  terminal  station,  to  effect  a  capacity  balance. 


336  AMERICAN  TELEGRAPH  PRACTICE 

The  proper  value  of  retarding  resistance  to  have  in  condenser  circuits  of 
multiplex  lines,  as  a  general  thing,  is  determined  by  the  length  of  the  line:  the 
longer  the  line,  or  the  greater  its  electrostatic  capacity,  the  greater  should  be 
the  amount  of  resistance  inserted;  for,  as  before  stated,  it  requires  a  longer  time 
to  discharge  long  lines  than  it  does  short  ones. 

The  steps  which  it  is  necessary  to  take  to  establish  a  static  balance,  in  any 
given  case  will  depend  upon  the  availability  of  the  apparatus  of  the  set,  for 
the  purpose. 

.  In  the  case  of  a  quadruplex  set,  a  good  way  to  obtain  a  static  balance  is 
to  reduce  the  tension  of  the  spring  attached  to  the  armature  of  the  neutral 
relay  while  the  distant  station  has  the  short-end  battery  to  line.  Then  if 
the  circuit  is  "out  of  balance,"  reversing  repeatedly  the  entire  home  battery 
will  result  in  more  or  less  pronounced  "kicks"  of  the  relay  armature.  These 
kicks  may  be  silenced  by  adjusting  the  capacity  of  the  condensers  and  the 
resistance  of  the  retardation  coils  until  a  capacity  balance  has  been  established. 
Ordinarily  the  entire  operation  can  be  completed  in  less  than  a  minute,  but 
as  it  is  essential  to  obtain  a  correct  static  balance,  sufficient  time  should  be 
taken  in  all  instances  to  accomplish  the  desired  end. 

In  balancing  duplexes  not  equipped  with  differential  galvanometers  or 
neutral  relays  for  balancing  purposes,  it  is  customary  to  touch  the  arma- 
ture of  the  polar  relay  with  a  pencil  or  with  the  finger  while  the  home  battery 
is  reversed,  and  to  observe  any  tendency  on  the  part  of  the  armature  to 
respond  to  the  reversals.  This  operation  may  be  carried  on  either  with  the 
distant  battery  to  line  and  quiet,  or  with  the  line  "grounded"  at  the  distant 
station. 

When  the  "static"  balance  is  being  taken  an  incorrect  amount  of  retard- 
ing resistance  is  evidenced  by  a  "kick"  in  one  of  the  relay  coils.  If  the  kick 
cannot  be  eliminated  by  altering  the  capacity  of  the  condensers,  or  if  it 
simply  shifts  from  one  side  to  the  other,  altering  the  amount  of  retarding 
resistance  in  series  with  each  condenser,  thus  properly  "  timing  "  the  discharge, 
quickly  remedies  the  trouble. 

POSTAL  TELEGRAPH-CABLE  COMPANY'S  RULES  FOR  BALANCING 
To  balance  a  duplex: 

"i.  Ask  the  distant  station  to  'ground.' 

"  2.  Throw  ground  switch  at  home  station  to  the  left. 

"3.  Set  the  armature  of  the  polar  relay  in  the  center  by  adjusting  the  magnets 
until  the  armature  will  remain  on  either  contact,  or  until  it  vibrates  freely  in 
response  to  the  induced  currents  from  the  line. 

"4.  Throw  the  home  station  ground  switch  back  to  the  right,  thus  placing  the 
current  on  the  line.  Take  a  line  balance;  that  is,  adjust  the  resistance  in  the 
rheostat  until  the  polar  relay  again  acts  as  it  did  when  the  line  was  to  ground  at 
both  ends.  This  line  balance  should  be  tried  with  the  home  key  first  open  and  then 


W.  U.  RULES  FOR  BALANCING-  337 

closed.  If  there  is  any  variation  in  the  resistance  required  to  effect  a  balance,  an 
average  should  be  made. 

"5.  Take  a  static  balance  in  the  following  manner:  Move  the  magnet  of  the 
polar  relay  which  is  on  the  opposite  side  of  the  local  contact  point,  or,  in  other 
words,  the  magnet  on  the  side  upon  which  the  armature  rests  when  the  sounder  is 
open,  1/4  to  3/8  of  an  inch  back.  Then,  starting  with  all  of  the  capacity  inserted 
in  the  condensers,  make  dashes  with  the  key  and  gradually  reduce  the  capacity 
until  the  kick  disappears.  A  variation  in  the  adjustable  resistance  in  the  condenser 
circuits  will  sometimes  aid  in  accomplishing  this  result.  After  removing  the 
kick  replace  the  magnet  in  its  former  position. 

"If  a  balance  indicator  is  used,  take  the  line  balance  by  adjusting  the  rheostat 
(see  Paragraph  4)  until  the  galvanometer  needle  points  to  zero  with  either  open  or 
closed  key  at  home  station." 

To  balance  a  quadruplex : 

"  Follow  the  method  described  for  duplex  up  to  end  of  Paragraph  4. 

"  Following  this  ask  the  distant  station  to  cut  in  and  dot  or  write  on  the  neutral 
or  common  side.  With  the  home  keys  quiet  the  neutral  relay  spring  tension  should 
be  adjusted  as  low  as  it  will  go  and  still  clearly  produce  the  signals  from  the  distant 
station.  The  home  battery  should  then  be  reversed  and  if  this  makes  the  signals 
from  the  distant  station  heavier  or  lighter  the  rheostat  should  be  adjusted  until 
the  reversal  of  the  home  battery  does  not  affect  them. 

"To  obtain  a  static  balance:  Ask  the  distant  station  to  open  his  key  on  the 
common  side,  thus  placing  his  short-end  to  the  line.  Close  the  common  side  key  at 
the  home  station.  With  the  distant  keys  quiet  the  neutral  relay  spring  tension 
should  be  adjusted  very  low  and  the  condensers  adjusted  until  reversals  of  the  home 
battery,  no  matter  how  rapid,  do  not  affect  the  neutral  relay." 

THE  WESTERN  UNION  TELEGRAPH  COMPANY'S  RULES  FOR  BALANCING 

Balancing  the  quadruplex:   • 

"The  usual  practice  of  balancing  to  the  distant  "ground"  on  quadruplex 
circuits  is  now  regarded  as  unnecessary,  owing  to  the  presence  in  the  circuit  of 
the  milliammeter,  which  admits  of  the  balances  being  taken  against  the  distant 
battery  with  less  loss  of  time,  and  under  conditions  that  eliminate  all  difference 
that  may  happen  to  exist  between  the  ground  and  battery  resistance." 

Resistance  balance: 

"In  taking  a  resistance  balance,  proceed  as  follows: 

"i.  Ask  the  distant  station  to  close  both  keys  which  will  cause  the  milliam- 
meter at  the  home  station  to  deflect  to  the  left,  or  in  what  may  be  called  a  marking 
direction. 

"2.  Note  the  number  of  degrees  obtained  on  the  needle,  first  with  your  No.  i 
key  open,  and  then  with  it  closed,  the  deflection  in  each  case  being  taken  after  the 
needle  has  come  to  rest. 

"3.  While  the  key  is  in  the  closed  position,  adjust  the  balancing  resistance 
22 


338  AMERICAN  TELEGRAPH  PRACTICE 

until  the  needle  reaches  a  point  midway  between  the  two  readings  above  noted, 
which  point  will  represent  the  deflection  required  to  secure  the  ohmic  or  resistance 
balance.  If,  for  instance,  the  needle  stands  at  28°  on  the  open  key,  and  at  24°  on 
the  closed  key,  then  the  adjustment  should  be  such  as  to  bring  the  needle  to  a 
position  that  will  correspond  as  nearly  as  possible  with  the  mean  of  the  above  two 
readings,  viz.,  26°. 

"It  will  be  found  that  when  the  resistance  in  the  artificial  line  is  greater  than 
that  in  the  main  line,  the  needle  will  swing  somewhat  deliberately  in  an  upward 
or  spacing  direction  upon  closing  the  key.  And,  per  contra,  the  swing  of  the  needle 
will  be  in  the  downward  or  marking  direction  should  the  resistance  in  the  artificial 
line  be  less  than  that  in  the  main  line." 

Static  balance: 

"It  will  next  be  in  order  to  take  a  'static'  balance,  any  disturbance  of  which 
will  make  itself  evident  by  a  sudden  throw  of  the  milliammeter  needle,  which  will 
quickly  jerk  or  'kick'  in  one  direction  just  as  the  key  is  being  depressed,  and  in 
the  opposite  direction  at  the  moment  the  key  is  released,  the  needle  instantly 
returning  to  its  normal  or  steady  position  after  each  movement  of  the  reversing 
key. 

"In  order  to  avoid  confusion  during  these  balancing  operations,  it  will  be  well 
to  disregard  the  effects  produced  upon  the  needle  at  the  opening  of  the  key,  and 
take  note  only  of  those  observed  at  the  closing  thereof. 

"i.  If,  then,  upon  closing  the  key,  the  needle  swings  or  kicks  in  a  spacing  or 
upward  direction,  and  then  rapidly  returns  to  its  former  fixed  position,  it  will  be 
an  indication  that  the  capacity  of  the  condensers  in  the  artificial  or  compensating 
circuit  is  not  enough,  and  should  accordingly  be  increased. 

."  2.  If,  on  the  other  hand,  the  throw  of  the  needle  is  in  the  downward  or  marking 
direction  at  the  instant  of  depressing  the  key,  the  condenser  capacity  should  be 
diminished. 

"The  amplitude  of  the  swing  or  kick  in  each  case  will  show  the  extent  or  amount 
of  the  static  unbalance,  the  latter  depending  upon  the  difference  between  the  strength 
of  that  portion  of  the  current  which  suddenly  rushes  into,  and  charges  any  main 
line  possessing  electrostatic  capacity,  and  that  of  the  current  rushing  into  the 
artificial  line  to  satisfy  the  "capacity"  requirements  of  the  condenser  forming 
part  of  the  compensation  circuit." 

Retardation  balance: 

"If  the  retarding  resistances  in  the  paths  of  the  balancing  condensers  are  not 
accurately  adjusted  the  time  occupied  in  charging  and  discharging  the  condensers 
will  differ  from  that  required  to  charge  and  discharge  the  main  line.  Should  this 
difference  be  very  pronounced,  the  milliammeter  will  give  a  peculiar  'double  kick' 
each  time  the  key  is  opened  and  closed,  this  kick  being  readily  distinguished  from 
that  due  to  the  ordinary  static  unbalance,  in  having  a  decidedly  more  jerky  and 
lively  appearance  during  its  exceedingly  brief  period  of  existence.  It  may,  however, 
be  somewhat  difficult  to  differentiate  between  the  two,  on  account  of  the  constant 
vibration,  to  which  the  milliammeter  needle  is  ordinarily  subjected  by  induction 


QUADRUPLEX  MANAGEMENT  339 

from  neighboring  wires,  the  effects  of  such  interference  rendering  accurate  reading 
and  close  observations  a  matter  of  considerable  difficulty.  Under  such  circum- 
stances, it  may  be  well  to  make  the  final  compensating  adjustments  by  rapidly 
dotting  on  the  No.  i  key,  while  making  such  alterations  of  the  capacity — and 
particularly  of  the  timing  or  retardation  resistances — as  will  cause  the  needle  to 
show  the  least  amount  of  disturbance  as  a  result  of  the  changes  thus  made." 

Approximate  balances: 

"An  absolutely  perfect  balance  cannot  be  secured  until  the  needle  ceases  to  be 
influenced  by  the  operations  of  the  reversing  key,  the  steady  condition  of  the  needle 
denoting  that  an  equality  of  potential  (upon  which  the  bridge  principle  depends) 
has  then  been  duly  established  "or,  in  other  words,  that  the  pressures  exerted  by 
the  out-going  current  at  opposite  ends  of  the  'bridge ' — in  which  the  milliammeter 
and  polar  relay  are  placed — are  equal  in  magnitude  and  oppositely  directed,  thus 
producing  a  null  effect  upon  both  of  those  instruments. 

"An  absolutely  perfect  balance  being  somewhat  difficult  of  attainment — 
especially  when  the  time  involved  is  an  important  consideration — it  is  only  neces- 
sary as  a  rule  to  obtain  a  good  working  balance,  that  is,  one  in  which  the  clearness 
and  legibility  of  the  in-coming  signals  are  practically  unaffected  by  the  out-going 
current. 

"It  should  not  be  necessary  in  most  cases  to  call  in  the  aid,  and  await  the  ap- 
pearance of  any  traffic  or  repeater  chief  at  a  distant  station  for  the  purpose  of 
restoring  a  balance,  which  can  usually  be  effected  by  suitable  'snap-shot'  adjust- 
ments calculated  to  meet  the  practical  working  requirements,  without  involving  a 
stoppage  of  the  circuit,  or  the  delay  incident  to  securing  the  attendance  of  the 
particular  chief  concerned  at  either  the  repeater  or  terminal  office." 

NOTES  ON  QUADRUPLEX  MANAGEMENT  AND  OPERATION. 

Difference  of  Balance,  Pole-changer  Key  Open  and  Closed. — At 

times  it  is  found  that  the  amount  of  resistance  necessary  to  have  in  the 
rheostat  to  balance  the  line  resistance  when  the  polar-side  key  is  closed, 
differs  from  that  necessary  to  maintain  a  balance  when  the  key  is  open. 

Since  the  closing  of  the  key  results  in  sending  out  currents  of  one  polarity, 
say  negative,  and  the  opening  of  the  key  sends  out  positive  currents,  it  is 
evident  that  the  difficulty  referred  to  is  due  to  the  presence  in  the  main-line 
wire,  of  a  current  of  definite  polarity  which  has  leaked  into  the  circuit  from 
a  neighboring  conductor,  or  to  a  difference  of  potential  between  the  home 
and  the  distant  ground  connection  due  to  earth  currents.  Assume  for 
instance,  that  a  foreign  potential  of  7  volts  positive  is  impressed  upon  the 
line;  in  one  position  of  the  pole-changer  armature  7  volts  are  added  to  the 
operating  potential,  while  in  the  other  position  of  the  armature  7  volts 
oppose  a  like  amount  of  the  applied  e.m.f.,  thereby  causing  a  difference  of 
14  volts  between  "open"  key  and  "closed"  key,  and  as  no  foreign  voltage 
affects  the  artificial  line,  the  variation  in  pressure  affects  the  main-line  circuit 
only. 


340  AMERICAN  TELEGRAPH  PRACTICE 

As  a  normal  ground  is  getting  to  be  the  exception  rather  than  the  rule, 
these  discrepancies  are  frequently  encountered,  and  the  usual  procedure 
is  to  halve  the  discrepancy  in  resistance  required  to  balance  with  key  opened 
and 'with  key  closed. 

Line  Capacity  too  High  to  be  Balanced  with  Total  Capacity  of  Con- 
densers.— When  a  quadruplex  attendant  finds  it  impossible  to  eliminate  the 
B-side  "kick"  by  adjusting  the  retardation  resistances,  and  by  employing  all 
of  the  artificial  capacity  available,  in  many  cases  the  difficulty  will  be  found 
to  be  attributable  to  the  fact  that  the  line  wire  in  use  is  "crossed"  with 
another  line  wire,  and  that  the  other  wire  has  been  thrown  out  of  service  by 
opening  it  at  each  of  the  two  terminal  stations.  When  this  is  done  the  cir- 
cuit operated  has  a  total  capacity  consisting  of  the  combined  capacity  of  both 
wires,  and  in  many  cases  this  is  greater  than  that  of  the  balancing  con- 
denser :  obviously,  the  remedy  is  to  have  the  discarded  wire  opened  on  each 
side  of  the  "cross"  as  near  to  the  point  of  contact  as  possible,  in  order  to 
reduce  the  superficial  area  of  the  conductor;  and  as  a  consequence  corre- 
spondingly repluce  the  total  capacity  of  the  circuit  being  operated. 

Whether  to  Raise  or  Lower  Compensating  Resistance  in  Order  to 
Obtain  a  Balance. — In  attempting  to  balance  a  duplex  or  quadruplex,  the 
beginner  is  often  in  doubt  as  to  whether  the  resistance  of  the  artificial  line 
should  be  increased  or  decreased  in  order  to  equal  that  of  the  line  wire. 

The  older  quadruplex  attendants  have  little  difficulty  in  this  regard  as 
they  know  from  experience  the  approximate  resistances  of  the  lines  in  their 
districts  and  are  therefore  enabled  to  quickly  move  the  rheostat  arms  into 
the  desired  positions.  The  younger  men  who  have  not  yet  had  an  oppor- 
tunity to  acquire  this  detail  information,  have  to  "feel"  their  way,  as  it 
were,  in  giving  the  compensation  circuit  the  desired  values. 

One  way  to  decide  the  matter  is :  after  the  distant  office  has  upon  request 
grounded  the  line,  the  attendant  at  the  home  station  should  note  whether  the 
armature  of  his  polar  relay  is  in  connection  with  the  open  or  closed  contact 
post.  If;  for  instance,  in  the  open  position,  move  the  rheostat  lever  of  the 
i  ,ooo-ohm  units  from  zero  around  toward  the  higher  values  until  the  arma- 
ture of  the  relay  moves  over  to  the  opposite  contact  post.  The  looo-ohm-unit 
lever  should  then  be  moved  back  one  point,  after  which  the  loo-ohm  units 
and  lo-ohm  units  should  be  added  until  an  exact  balance  is  obtained. 
•  Negative  Pole  to  Line  on  Closed  Key. — In  the  interests  of  standardiza- 
tion and  of  interchangeability  of  sets  it  is  well  to  arrange  all  duplex  and 
quadruplex  pole-changer  circuits  so  that  they  will  send  out  the  same  polarity 
when  keys  are  open,  and  the  opposite  polarity  when  keys  are  closed. 

The  reason  advanced  for  selecting  the  negative  pole  as  the  "closed" 
pole  is  that:  due  to  the  periods  of  rest  and  of  inaction,  pole-changer  arma- 
tures are  in  the  open  position  a  greater  length  of  time — in  the  aggregate — than 
in  the  closed  position,  and  as  current  from  the  positive  terminal  of  the  bat- 


LOCATING  FAULTS  IN  QUADRUPLEX  APPARATUS      341 

tery  is  less  destructive  to  cable  insulation  than  that  from  the  negative  terminal, 
it  is  good  economy  to  connect  the  positive  battery  lead  to  the  "op'en"  con- 
tact of  the  pole-changer. 

LOCATING  FAULTS  IN  DUPLEX  AND  QUADRUPLEX  APPARATUS 

Faults  may  develop  in  a  duplex  or  a  quadruplex  set  in  one  or  more  of  a 
number  of  places.  Those  faults  which  cause  entire  failure  generally  are  the 
easiest  to  locate  and  remedy.  Faults  which  only  partially  interfere  with 
operation  of  the  set  are  more  difficult  to  run  down,  and  in  practice  are  less 


Open 


385Volts 
+ 

Transm'f'r 
9 00  Oh  mi 
fWjW—v 


Cond'r: 

V       pS  Rheostat 
16   J/G 


Polechanger 


Neutral 
Retay  A 


FIG.  292. — Quadruplex  apparatus  tests. 


likely  to  be  given  due  attention.  A  defective  relay,  rheostat,  condenser  or 
resistance  coil  may  result  in  the  unsatisfactory  operation  of  a  set  without 
the  trouble  being  sufficiently  pronounced  to  justify  abandoning  the  set  as  a 
"  four-cornered  "  system. 

The  plan  of  set  testing  here  described  is  one  recently  sent  out  by  Mr. 
Minor  M.  Davis,  Electrical  Engineer  of  the  Postal  Telegraph-Cable  Com- 
pany, and  which  in  practice  has  been  found  to  give  excellent  results. 


O  O  O      ©  <D  ©  © 


000®      OO 


Polar  Relay.  Neutral  Relay. 

FIG.  293. — Quadruplex  apparatus  tests. 

First,  measure  the  total  resistance  of  the  balancing  coils  of  a  spare 
rheostat  to  make  sure  it  is  not  defective.  Then,  at  the  main  board,  place  the 
line  wedge  from  the  set  to  be  tested  in  a  grounded  "flip,"  in  series  with  the 
spare  rheostat.  Make  the  resistance  of  the  rheostat  at  the  switchboard 
2,000  ohms.  Then  balance  the  rheostat  of  the  set  against  the  one  at  the 


342  AMERICAN  TELEGRAPH  PRACTICE 

switchboard.  After  securing  an  ohmic  balance  (a  static  balance  is  not 
needed),  allow  the  long-end  to  remain  closed  a  few  minutes  to  heat  up  the  coils, 
and  develop  circuit  defects  should  there  be  any.  When  the  set  has  warmed  up, 
take  a  voltmeter  which  has  a  single  conductor  cord  and  wedge  connected 
to  each  of  its  terminals,  to  the  set  to  be  examined,  and  after  changing  the 
resistance  of  the  rheostat  at  the  switchboard  to  5,000  ohms,  take  a  new 
balance  as  quickly  as  possible,  and  proceed  as  follows : 

Using  Lower  Scale  of  Voltmeter. — If  voltage  between  A  and  B  (Figs. 
292  and  293)  is  the  same  as  between  A  and  D,  the  neutral  relay  is  OK.  If 
the  voltage  between  B  and  C  is  the  same  as  between  D  and  E,  the  polar  relay 
is  OK. 

Using  the  Upper  Scale  of  the  Voltmeter. — The  voltage  between  A  and  C 
should  equal  the  voltage  between  A  and  E. 

TO  TEST  THE  CONDENSERS 

Using  Upper  Scale  of  Voltmeter. — If  the  voltage  between  E  and  the  ground 
is  the  same  when  all  of  the  condenser  capacity  is  "cut  in"  as  when  all  "cut 
out,"  the  condensers  are  OK.  If  not,  they  are  leaky. 

Another  way  to  test  the  condensers  is  to  cut  out  all  of  the  capacity  and 
and  open  both  the  ground  switch  and  the  balancing  rheostat.  Then  touch 
the  line  wedge  to  either  battery  terminal.  If  a  condenser  is  short-circuited 
the  neutral  relay  armature  will  be  attracted  into  the  closed  position. 

CROSSED  WINDINGS  IN  EITHER  RELAY 

The  introduction  of  a  two-point  switch  (normally  closed)  in  the  artificial- 
line  circuit,  between  the  dividing  point  of  the  main  and  artificial  lines  and  the 
neutral  relay,  enables  the  attendant  to  test  out  crossed  windings  in  the  fol- 
lowing manner:  Remove  the  line  wire  from  the  binding-post  C,  then  open 
the  two-point  switch  A  (in  the  absence  of  a  switch,  the  test  may  be  made 
by  removing  the  wire  from  the  binding-post  A).  If  the  windings  of  either 
relay  are  crossed,  the  armatures  of  the  relays  will  respond  to  the  movements 
of  the  pole-changer  key. 

MEASURING  THE  DISTANT  BATTERY 

The  information  sought  in  measuring  the  quadruplex  battery  at  the  distant 
terminal  station  is:  whether  both  polarities  are  being  sent  to  line  alternately 
as  the  pole-changer  key  at  the  distant  station  is  operated:  whether  the 
current  received  from  the  distant  battery  is  of  sufficient  strength  to  operate  the 
relays,  and  whether  the  long-end  and  short-end  from  the  distant  station 
divide  in  the  proper  proportions  of  3  to  i,  or  4  to  i  as  the  case  may  be. 

The  measurements  desired  are,  of  the  short-end  positive  current,  short- 
end  negative  current,  long-end  positive  current,  and  long-end  negative 
current. 


MEASURING  DISTANT  BATTERY  343 

(1)  Insert  the  double  wedge  connected  by  cord  to  the  milliammeter  in  the 
main-line  circuit,  either  between  the  line  wire  and  main-line  binding  post  of 
the  polar  relay,  or  between  the  line  post  and  ground  post  of  the  ground  switch. 

(2)  Tell  the  distant  station  to  close  his  key  on  both  polar  and  neutral  sides. 
The  reading  observed  in  the  meter  will  be  that  due  to  the  long-end  negative 
potential ,  assuming  that  the  negative  pole  is  to  line  on  closed  key. 

(3)  Cut  in  the  home  battery  for  a  minute  and  tell  the  distant  station  to 
leave  the  neutral-side  key  closed  and  to  open  the  key  on  the  polar  side.     The 
reading  observed  will  be  that  due  to  the  long-end  positive  potential — assuming 
that  the  positive  pole  is  to  line  on  open  key. 

(4)  Again  cut  in  the  home  battery  for  a  minute  and  tell  the   distant 
station  to  open  the  keys  on  both  polar  and  neutral  sides.     The  reading  ob- 
served will  be  that  due  to  the  short-end  positive  potential. 

(5)  Ask  the  distant  station  to  leave  the  neutral-side  key  open  and  to  close 
the  polar-side  key.     The  reading  observed  will  be  that  due  to  the  short- 
end  negative  potential. 

If  the  tests  are  made  by  inserting  the  wedge  between  the  line  wire  and  the 
main-line  binding-post  of  the  relay,  the  ground  switch  should  be  thrown  over 
to  the  " ground"  contact,  and  if  inserted  between  the  line  binding-post  and 
ground  binding-post  of  the  ground  switch,  the  lever  should  be  placed  in  the 
central  position  and  the  artificial-line  opened  as  each. reading  is  taken. 

On  account  of  the  ever  present  inductive  influences,  there  are  very  few 
lines  in  this  country  that  will  work  satisfactorily  with  less  than  20  milliam- 
peres,  and  with  a  3  to  i  proportion  the  long-end  would  need  to  yield  60  milli- 
amperes. 

It  is  of  the  utmost  importance  that  the  proper  " ratio"  should  be  main- 
tained, as  the  successful  operation  of  the  common  side  relay  is  dependent  upon 
the  difference  between  operating  and  releasing  current  values. 


CHAPTER  XVI 

DUPLEX  AND   QUADRUPLEX    "LOCAL"    CIRCUITS.    LEG-BOARD, 
AND  LOOP-BOARD  CONNECTIONS 

METHODS  OF  THE  POSTAL  TELEGRAPH-CABLE  COMPANY 

Figure  294  shows  theoretically  the  wiring  of  the  Postal  Telegraph-Cable 
Company's  duplex  and  quadruplex  "local"  circuits. 

On  the  left  in  the  center  is  shown  the  local  circuits  of  a  polar  duplex,  and  on 


BffAMCH  OrriCE  A  NO  0ROUNO  /3O  —  OH, 


THEORY  STANDARD  gUAORUPL £X  ANO  OUPL  fX  f?£PEA  T£f?  L£tf  JACtf  AND  L OCAL   CONNZC  T/ONS. 


FIG.  294. 

the  right  the  local  circuits  of  the  second  side  of  a  quadruplex.  The  local 
wiring  of  a  quadruplex  would  comprise  all  of  the  wiring  shown  in  the 
diagram. 

It  will  be  noted  that  there  are  two  six-point  switches  controlling  the  cir- 

344 


DUPLEX  AND  QUADRUPLEX  "LOCAL"  CIRCUITS         345 

cuit  arrangements  of  each  half  of  the  set.  In  each  half  of  the  set  the  switch 
on  the  left  controls  the  application  of  battery  to  the  sending  and  receiving  in- 
struments, while  the  switch  on  the  right,  in  each  case,  makes  it  possible  to 
extend  "legs"  from  the  sending  and  receiving  apparatus  of  each  half  of  the 
quadruplex,  to  a  leg-board  suitably  located  near  the  main  switchboard. 

The  leg-board  connections  are  shown  theoretically  at  the  top  of  the  dia- 
gram, and  it  will  be  seen  that  by  means  of  these  connections,  the  control  of 
the  pole-changer  of  the  duplex  (or  the  polar  side  of  a  quadruplex)  may  be  ex- 
tended to  an  operating  table  located  at  a  distance  from  the  quadruplex  set,  or 
to  a  branch  office.  And,  further,  that  the  signals  received  by  the  polar  relay 
of  the  duplex  (or  of  a  quadruplex)  may,  through  the  leg-board  connections, 
be  repeated  directly  to  a  sounder  situated  on  the  operating  table  above  re- 
ferred to,  or  to  a  sounder  situated  in  the  branch  which  may  have  been  given 
control  of  the  operation  of  the  pole-changer  of  the  set. 

Both  Local  Switches  to  the  Right. — Figure  295  is  a  simplified  diagram 
showing  the  completed  circuit  from  the  40  volt,  or  local  dynamo,  through 
the  pole-changer,  sounder,  key,  and  leg-board  to  ground.  While  the  local 
switches  are  to  the  right,  the  three  other  local  circuits  are  connected  in  the 
same  manner  as  the  pole-changer  is  shown  connected  in  Fig.  295. 


PJ 


Key 


FIG.  295. — Pole-changer  local  circuit  when  levers  of  both  table  switches  are  moved  to  the 

right. 

It  will  be  apparent  that  if  a  separate  transmitting  key  has  its  two  terminals 
connected  to  the  cord  terminals  of  a  double-conductor  wedge,  and  the  wedge 
is  inserted  in  the  spring- jack  SJ,  the  extra  key  will  have  control  of  the  opera- 
tion of  the  pole-changer  in  the  same  way  that  the  key  of  the  "set"  has  control 
of  that  circuit,  provided,  of  course,  that  the  latter  is  kept  closed. 

Also,  it  will  be  apparent  that  the  extra  key  may  have  one  of  its  terminals 
connected  to  a  single-conductor  wedge,  while  the  other  terminal  of  the  key 
is  "grounded,"  in  which  case  it  is  necessary  that  the  "live"  or  conductor 
side  of  the  wedge  be  placed  in  contact  with  the  shoe  of  the  spring-jack  (thus 
removing  the  ground  connection  via  the  shank  of  the  spring- jack,  and  the 
pin-jack  PJ).  In  the  first  case,  the  separate  key  would  be  regarded  as  being 
"looped"  in,  and  in  the  second  case,  as  being  "legged"  on. 

It  is  obvious  that  the  loop,  or  the  leg,  whichever  is  employed,  may  be 


346 


AMERICAN  TELEGRAPH  PRACTICE 


extended  to  a  table  in  the  operating-room,  remote  from  the  multiplex  set 
proper,  or  to  a  distant  branch  office. 

Both  Local  Switches  to  the  Left. — Figure  296  is  a  simplified  diagram 
of  the  circuit  conditions  which  exist  when  both  switches  are  thrown  to  the 
left.  This  is  the  position  in  which  the  switches  are  placed  when  the  set  is 
not  in  use. 

PJ 


1  , 

1 

1- 
-tvr 

H 

1 

5 

PC 

A*/ 

Tine 

1     1 

FIG.  296. — Pole-changer  local  circuit  when  levers  of  both  table  switches  are  moved  to  the 

left. 

Local  Switches  Thrown  "Together." — When  the  two  local  switches  on 
one  side  of  a  quadruplex,  or  in  a  duplex,  are  thrown  "together,"  that  is, 
the  left-hand  switch  to  the  right,  and  the  right-hand  switch  to  the  left,  the 
actual  circuit  connections  are  as  indicated  in  Fig.  297,  which  provides  that 
the  attendant  at  the  multiplex  set,  only,  will  have  control  of  the  local  cir- 
cuits, and  that  any  "legs"  or  "loops"  which  may  be  connected  into  the  cir- 
cuit at  the  spring-jack  SJ  will  be  cut  off  and  remain  so  until  the  right-hand 
switch  is  again  thrown  to  the  right. 


FIG.  297. — Pole-changer  local  circuit  when  levers  of   both    table    switches    are  thrown 

"together." 

Local  Switches  Thrown  "Apart." — When  both  local  switches  of  a 
duplex  or  a  quadruplex  set  are  thrown  "apart,"  as  shown  on  the  right  in 
Fig.  294,  a  loop  circuit  is  established  which  places  the  spring-jack  of  the 
"leg"  or  "loop"  board  in  series  with  the  other  local  connections,  as  indi- 
cated in  Fig.  298. 

This  arrangement  permits  of  connecting  two  grounded  single  circuits 
or  "legs"  and  one  or  more  loop  circuits  in  series  with  the  pole-changer 


DUPLEX  AND  QUADRUPLEX  "LOCAL"  CIRCUITS         347 

local,  so  that  a  number  of  branch  offices  may  be  given  control  of  the  latter 
instrument.  On  account  of  the  increased  resistance  of  the  local  circuit  due 
to  the  added  loops  and  legs  together  with  the  resistance  of  the  sounders 

?n  PJ 


S 5/ngle  Wedges 
'\fc----Double  Wedges 


Loop 


FIG.  298.— Pole-changer  local  circuit  when  levers  of  both  table  switches  are  thrown  apart 
for  the  purpose  of  including  an  extra  loop  and  two  grounded  legs. 


FIG.  299. 

included  in  each  additional  circuit,  the  regular  4o-volt  battery  is  replaced 
with  a  battery  of  about  100  volts,  both  terminals  of  which  are  connected  to  a 
double-conductor  wedge,  for  insertion  in  the  spring-jack  as  shown  in  Fig.  298. 1 

1  See    Fig.    270,  page  43,  and  the  description  there  given  of   intermediate  battery 
connections. 


348 


AMERICAN  TELEGRAPH  PRACTICE 


While,  in  Figs.  295,  296,  297  and  298  the  local  wiring  and  loop-board 
connections  of  a  pole-changer  are  shown,  it  is  to  be  understood  that  in  each 
illustration  the  pole-changer  might  be  replaced  by  the  "  transmitter  "  associ- 
ated with  the  second  side  of  a  quadruplex,  or  by  the  local  contacts  of  the 
polar  relay,  or  of  the  bug-trap  relay,  the  latter  representing  respectively 
the  receiving  circuits  of  the  polar  side  and  common  side  of  the  quadruplex. 

Figure  299  shows  the  actual  binding-post  connections  of  the  duplex 
and  quadruplex  where  no- volt  potentials,  and  i5o-ohm  local  instruments 
are  employed.  Where'  4o-volt  potentials  are  employed  the  i,5oo-ohm 
coils  are  omitted,  all  other  connections  remaining  the  same. 

Figure  300  is  a  photographic  reproduction  of  a  leg,  or  loop  switchboard 
in  one  of  the  Postal  Telegraph- Cable  Company's  offices.  Two  sections  of 
loopswitch  are  shown  in  the  left  half  of  the  photograph.  It  may  be  seen 


FIG.  300. — Two  sections -of  a  "Postal"  loop  board. 


that  at  the  extreme  upper  edge  of  each  board  there  is  a  row  of  pin-jacks, 
and  immediately  underneath  a  row  of  spring-jacks,  then,  in  order,  two  rows 
of  pin-jacks,  a  row  of  spring-jacks,  two  rows  of  pin-jacks,  a  row  of  spring- 
jacks,  followed  by  six  rows  of  pin-jacks  in  the  vertical  back-board,  and  six 
rows  of  pin-jacks  in  the  shelf  panel  underneath. 

Figure  301  shows  in  skeleton  the  connections  and  conductor  assignments 
of  the  various  pin-jacks  and  spring-jacks  of  this  loopswitch  in  the  order 
named. 


DUPLEX  AND  QUADRUPLEX  "LOCAL"  CIRCUITS         349 

WESTERN  UNION  QUADRUPLEX  LOCAL  AND  LOOPSWITCH  CONNECTIONS 

Figure  302  shows  a  diagram  of  the  local  circuits  and  loopswitch  con- 
nections of  a  duplex,  or  polar  side  of  a  quadruplex,  as  arranged  in  Western 
Union  service. 

With  the  switch  levers  in  the  positions  shown,  it  is  evident  that  the  loop 
extending  to  the  operating  table  in  the  main  operating-room,  or  to  a  branch 


Patching 


To  Ground  Coil 


FIG.  301. — Spring-jack  and  pin-jack  wiring  of  a  loop  board. 

office  has  been  cut  off,  in  order  that  the  quadruplex  attendant  alone  may 
have  control  of  the  apparatus,  for  the  purpose  of  balancing,  etc. 

Figure  303  shows  the  positions  of  the  local  switches  after  the  balance 
has  been  taken,  and  the  circuits  cut  through  to  the  operating  room  or  to  a 
branch  office.  The  connections  are  those  of  a  polar  duplex  or  of  the  polar 
side  of  a  quadruplex. 


350 


AMERICAN  TELEGRAPH  PRACTICE 


To  Branch  Office 
or  Office  Loop 


FIG.  302. — Western  Union  loopswitch  connections. 


FIG.  303. — W.  U.  loopswitch. 


FIG.  304.— W.  U.  loopswitch  connections  formterconnecting  multiplex  sets. 


DUPLEX  AND  QUADRUPLEX  "LOCAL"  CIRCUITS         351 

Figure  304  illustrates  the  positions  of  the  local  switches  for  connecting 
the  common  side  of  one  quadruplex  set  to  the  common  side  of  another 
quadruplex  set  for  the  purpose  of  repeating.  A  double  conductor  cord  with 
a  double  wedge  at  each  end  serves  to  connect  the  two  sets  together  through 


Note. :- "Pi  lot  TSeloM 
'for  AudibleSiqnal 
to  be  inserted  at 
point  "A  common 
to  not  more  than 
lit  lamps, as  per 
6pec.ificat.ion6 
•far  Siknali 


Note :  -  When 
.Signal  Relays 
are  not.  used, 
connect  a  to  b 
and   c,-to-<d 


FIG.  305. — Instrument  local  circuit  connections,  W.  U.  quadruplex. 

the  medium  of  the  proper  spring-jacks  in  the  loopswitch.  In  this  case  the 
positions  of  the  switch  levers  are  such  that  the  neutral  relay  of  each  set 
controls  the  operation  of  the  transmitter  of  the  other  set. 

Figure  305  shows  the  instrument  binding-post  connections  of  the  local 
circuits  and  loopswitch  wiring. 


352 


AMERICAN  TELEGRAPH  PRACTICE 
OPERATING  TABLE  AND  BRANCH -OFFICE  WIRING 


Figure  306  shows  five  loops  leading  from  a  main  switchboard,  each  loop 
connected  to  an  operating  set  at  a  table  in  the  main  operating-room  or  in  a 
branch  office,  in  each  case  arranged  to  meet  different  requirements. 


6Q-, 

ys 

*"            .Z^ 

SOUNDER 

1 

9 

A 

II 

GO*. 


PLAN  f~0f?  WIP./NB-  BRANCH 
OfT7CE3  3HOW/N8A4Of?SE  LOOP 
S/N&LE  Off  0  UPL  EX;  CO/V\B/NA  T/ON 


LOCALS. 


SW/TCHCS  TO  f?/BHTf~Df? /MORSE,  SWtTCHES  TQ  THE  LEFT  FVP.DIJPL  £~X£&* 


FIG.  306. — Operating  table  and  branch  office  wiring. 


FIG.  307.— Branch  office  instrument  arrangement  for  either  single  or  duplex  working, 
employing  two  loops  to  main  office. 

At  A  a  loop  is  connected  to  a  main-line  sounder  and  key  for  single-line 
operation  only. 

At  B  single-line  operation  only  is  provided  for,  but  in  this  case  a  relay  in 


BRANCH-OFFICE  INSTRUMENT  ARRANGEMENT 


353 


the  line  circuit  operates  a  sounder  locally  by  means  of  gravity  battery  con- 
nected through  the  local  contact  points  of  the  relay. 

At  C  the  arrangement  is  the  same  as  at  B  except  that  the  current  to  operate 
the  sounder  is  obtained  from  a  dynamo  instead  of  a  gravity  battery. 


• 

II 


RecVg 
5dr, 


PJ 


PJ 


i 

it 

1 

J 

K 

1"                                                             ^ 

mT           vl 

HH— 

»  Relay          dend'q                  j^ 
5dr                    w 

FIG.  308. — Branch  office  wiring  for  single  or  duplex  working. 


FIG.  309. — Branch  office  instrument  arrangement  for  either  single  or  duplex  working, 
employing  one  pair  of  conductors  to  the  main  office. 

At  D  provision  is  made  for  either  duplex  or  single  operation,  employing 
gravity  battery  to  operate  the  sounder  when  the  line  is  worked  single.  The 
switch  is  thrown  to  the  right  for  single,  and  to  the  left  for  duplex  operation. 

At  E  the  arrangement  is  the  same  as  at  D'except  that  dynamo  current  is 
used  to  operate  the  sounder  when  the  set  is  being  used  for  single-line  opera- 

23 


354 


AMERICAN  TELEGRAPH  PRACTICE 


tion.  In  each  case  55  signifies  " sending  sounder,"  and  RS  ''receiving 
sounder." 

Where  dynamo  current  is  employed  for  the  operation  of  sounders  at  branch 
offices  it  is  customary  to  run  a  local-battery  main  from  the  central  office  to 
the  branch  office  for  the  purpose. 

There  are  in  use  a  number  of  methods  of  branch-office  wiring,  all  of  which 
provide  for  single  or  duplex  working,  simply  by  shifting  the  position  of  the 
levers  of  a  six-point  switch.  Fig  307  shows  an  arrangement  of  circuits 
which  may  be  employed  where  a  sending  loop  and  a  receiving  loop  extend  from 
the  main  to  the  branch  office.  Moving  the  switch  levers  to  the  right  makes 
possible  the  use  of  the  "sending"  loop  for  single-line  operation,  while  moving 


FIG.  310. — Branch  office  arrangement  for  single  or  duplex  working,  using  two  6-point 

switches. 

the  levers  to  the  left  provides  for  duplex  operation  by  utilizing  both  loops; 
the  one  on  the  right  including  the  key  and  one  sounder  for  transmitting 
purposes,  and  the  sounder  on  the  left  serving  as  a  receiving  sounder.  In  the 
diagram  the  wiring  at  the  branch  office  only  is  shown. 

Figure  308  shows  a  similar  arrangement,  and  which  accomplishes  the 
same  purpose.  The  receiving  sounder  has  attached  to  its  terminals  a  flexible 
double-conductor  cord  to  the  outer  end  of  which  is  connected  a  double  plug 
for  insertion  into  the  pin-jack  to  the  right  when  the  relay  is  connected  into  a 
single  line,  and  into  the  pin-jack  on  the  left  when  a  duplexed  circuit  is  to  be 
operated  from  the  branch  office. 

Throwing  the  switch  to  the  right  provides  for  single-line  operation,  while 
the  reverse  movement  provides  for  duplex  operation. 

Figure  309  shows  an  arrangement  using  one  switch  and  one  pair  of 
conductors  between  the  main  and  branch  offices.  At  the  main  office  a  "half- 
tap"  is  made  connecting  each  side  of  the  loop,  on  the  one  hand  to  a  double 
pin-jack  in  the  main  board,  and  on  the  other  to  two  separate  single  pin-jacks 
in  the  leg-board.  As  in  the  other  methods  illustrated,  moving  the  switch 


BRANCH-OFFICE  INSTRUMENT  ARRANGEMENT 


355 


levers  to  the  right  provides  for  single-line  operation,  while  moving  them  to 
the  left  provides  for  duplex  operation. 

Figure  310  depicts  an  arrangement  of  circuits  in  which  two  6-point 
switches  are  employed  at  the  branch  office,  and  where  one  pair  of  conductors 
extends  between  the  main  and  branch  offices.  Throwing  the  levers  to  the 
right  provides  for  single-line  operation,  while  placing  the  switches  in  the 
opposite  position,  as  shown  in  the  diagram,  provides  for  duplex  operation. 


FIG.  311. — Branch  office  arrangement  for  single  or  duplex  working,  where  no-volt  local 

current  is  used. 

Figure  311  shows  a  "combination"  set  for  single  or  duplex  service,  in 
use  where  no-volt  local  battery  is  employed  for  the  operation  of  local  cir- 
cuits. At  the  main  office,  i,5oo-ohm  resistance  coils  are  inserted  in  each 
1 10- volt  battery  lead,  and  at  both  main  and  branch  offices  i5o-ohm  in- 
struments are  used.  When  the  switch  is  in  the  position  shown  in  the  dia- 
gram the  circuit  is  arranged  for  duplex  operation,  and  when  thrown  to  the 
right  the  branch-office  ground  connection  is  removed  and  the  main-line 
sounder  and  transmitting  key  are  connected  in  series  in  the  loop  extending 
to  the  main  office  so  that  the  set  may  be  used  for  single-line  operation. 


CHAPTER  XVII 


BRANCH-OFFICE  ANNUNCIATORS.  GROUPING  OF  WAY-OFFICE 
AND  BRANCH-OFFICE  CIRCUITS— NEEDHAM  ANNUNCIATOR. 
OFFICE  SIGNALING  SYSTEMS  FOR  MULTIPLEX  CIRCUITS. 
BELL-WIRES.  MAIN-LINE  CALL  BELLS,  SECOND  SIDE  OF 
QUADRUPLED  SELECTORS 

When  main-line  circuits  are  extented  through  to  broker  offices,  news- 
paper offices,  or  branch  commercial  offices  by  means  of  loops  from  the  main 
office,  it  is  not  always  practicable  to  have  attendants  at  the  latter  office  to 
constantly  observe  the  operation  of  such  circuits  in  order  to  be  on  hand  when 
interruptions  occur.  In  order  to  provide  branch  offices  with  a  means  of  call- 
ing an  attendant  at  the  central  office  to  the  circuit  in  trouble,  it  is  customary 
to  maintain  at  the  latter  office  a  "bank"  of  annunciators  through  the  wind- 
ings of  which  the  various  loops  may 
be  connected.  The  annunciator  may 
be  operated  by  pressing  a  contact 
button  or  closing  a  switch  at  the 
branch  office,  resulting  in  the  release 
of  the  shutter  or  tablet  of  the  annun- 
ciator connected  into  that  particular 
circuit.  The  falling  of  the  shutter 
exposes  to  view  a  marker  bearing 
the  name  of  the  brokerage  firm,  the 
number  of  the  wire,  or  the  call  of 
the  office  signaling  for  attention. 
As  usually  arranged  the  shutter  in 


Line 


1s 


I  branch  Office 

//rnwl 


FIG.  312.— Branch  office  signaling  annunciator,  falling   closes   a  local  circuit  which 

includes  an  electric  bell,  a  miniature 

incandescent  lamp,  or  both,  in  order  to  insure  quick  response  at  the  main 
office. 

A  simple  arrangement  sometimes  employed  is  illustrated  theoretically  in 
Fig.  312,  which  shows  an  individual  "straight-wound"  magnet  annunciator 
at  the  main  office,  having  a  resistance  of  2  ohms.  The  tablet  T  is  pivoted  at 
P,  while  the  armature  A  is  rigidly  connected  at  P'  with  a  light  rod  R  extending 
along  the  top  of  the  magnet,  and  fitted  with  a  hook,  which,  due  to  gravity, 
retains  the  tablet  in  the  upright  position  when  the  annunciator  magnet  is  not 
energized  sufficiently  to  attract  its  armature.  As  the  2  -ohm  annunciator  mag- 

356 


BRA  NCH-OFFICE  A  NN  UN  CIA  TORS 


357 


net  requires  at  least  five  times  as  much  current  to  attract  its  armature  as  the 
i5o-ohm  relays  in  the  circuit  require  for  their  operation,  it  is  plain  that  as 
long  as  the  ordinary  current  strength  obtains  in  the  circuit  the  armature  of 
the  annunciator  will  not  be  attracted.  Should  the  branch  office,  however, 
move  the  lever  of  the  switch  S  into  contact  with  the  ground  connection,  the 
total  resistance  presented  to  the  battery  will  be  greatly  reduced  with  the  re- 
sult that  the  current  in  the  circuit  instantly  builds  up  to  a  strength  sufficient 
to  energize  the  annunciator  magnet,  causing  its  armature  to  be  attracted,  re- 
leasing the  tablet  T,  which,  coming  into  contact  with  the  metal  terminal  C 
closes  a  local  circuit  which  includes  an  electric  bell.  At  the  branch  office  the 
switch  S  needs  only  to  touch  the  ground  contact  momentarily  to  accomplish 
its  purpose.  The  attendant  at  the  main  office  upon  hearing  the  bell  connects 
his  test  set  into  the  proper  circuit  and  restores  the  tablet  to  the  upright 
position. 

THE  DIFFERENTIAL  ANNUNCIATOR 

Figure  313  shows  the  actual  main-office  and  branch-office  connections  of  an 
arrangement  extensively  employed  by  the  Postal  Telegraph- Cable  Company 


FIVE  POINT  SWITCH  IS  THROWN  TO  LEFT  TO  CALL  AHIAIM 
•fFFICE  ANO  0&OI/A/0  ONE  SIOEOFLOOP. 
WEOG-E  ISftEVERSEO  TO  USE  OTHER  S/OC  OF  LOOP  TO 


FIG.  313. — Differential  annunciator. 

in  which  the  annunciator  at  the  main  office  has  two  identical  windings;  one  in 
each  side  of  the  loop. 


358 


AMERICAN  TELEGRAPH  PRACTICE 


To  operate  the  device,  the  levers  of  the  five-point  switch  at  the  branch 
office  are  moved  to  the  extreme  left  position  and  back  again  to  the  right.  It 
is  apparent  that  this  operation  momentarily  grounds  one  side  of  the  loop  thus 
permitting  a  greater  volume  of  current  to  flow  in  one  winding  of  the  annunci- 
ator than  flows  through  the  companion  winding,  resulting  in  the  attraction 
of  the  armature  and  the  release  of  the  tablet. 

Should  trouble  develop  in  the  loop,  it  is  apparent  that  by  placing  the  levers 
of  the  five-point  switch  to  the  left,  one  side  of  the  loop  may  be  worked  to  a 
ground  at  the  branch  office.  Reversing  the  wedge  W  in  the  spring-jack  at 
the  branch  office  permits  of  using  either  side  of  the  loop  in  series  with  the 
branch-office  relay  and  key. 

ANNUNCIATOR-BOARD  CONNECTIONS 

Figure  314  shows  the  magnet  and  pin-jack  connections  of  one  annunciator 
unit  at  the  main  office  where  the  differential  system  is  employed.  Pin-jacks 


FIG.  314. — Annunciator-board  connections.     Differential  annunciator. 

1,2,  and  3  are  normally  closed,  and  are  used  to  connect  test  Morse  sets  into 
the  circuit,  or  to  connect  additional  loops  in  series  with  that  particular  line 
by  means  of  double-conductor  plugs  attached  to  flexible  cords.  Pin-jacks 
4  and  5  are  normally  open,  and  are  used  for  applying  battery  or  ground  con- 


BRA  NCR-OFFICE  A  NN  UN  CIA  TORS 


359 


nections  at  the  annunciator  board  as  desired.  Pin-jacks  6  and  7  are  located 
close  together  so  that  a  comparatively  short  cord  may  be  used  to  make  the 
regular  assignment  connection  between  a  particular  branch-office  loop  and  a 
particular  main-line  wire.  The  re-set  pin-jack  shown  beneath  the  annunciator 
magnet  is  the  one  usually  availed  of  by  the  annunciator  attendant  to 
connect  his  Morse  set  into  the  circuit  when  he  is  signalled  in.  Insertion  of 
the  plug  in  the  re-set-jack  automatically  restores  the  tablet  (not  shown)  to 
the  upright  position. 

GROUPING  WAY-OFFICE  AND  BRANCH -OFFICE  CIRCUITS 

In  nearly  all  large  telegraph  offices  there  are  many  individual  circuits 
having  one  or  more  offices  connected  therein,  which  do  not  have  a  sufficient 
amount  of  business  passing  over  them  to  justify  the  continuous  attention  of 
an  operator  on  each  such  circuit,  at  the  main  office.  The  traffic  problem  here 
presented  consists  in  giving  reasonably  prompt  service  to  the  various  out- 
lying offices  with  the  minimum  number  of  operators  at  the  main  office. 


FIG.  315. — Branch  office  signaling  arrangement_for  concentrated  circuits. 

There  are  several  somewhat  different  circuit-concentrating  methods  em- 
ployed for  the  purpose  of  meeting  these  conditions,  all  of  which  are  identical 
in  certain  respects. 

In  the  service  of  both  the  Western  Union,  and  the  "Postal"  companies 
it  is  customary  to  mount  a  number  of  annunciators  along  the  center  of  an 
operating  .table,  each  annunciator  being  connected  in  circuit  with  a  separate 


360  AMERICAN  TELEGRAPH  PRACTICE 

branch  office,  or  short  line  wire,  and  so  located  with  respect  to  the  position  of . 
the  operator,  that  one  man  can  conveniently  answer  calls  upon  a  number  of 
circuits,  similarly  to  the  manner  in  which  a  central  telephone-office  operator 
can  answer  calls  from  a  number  of  telephone  stations,  that  is,  by  inserting  a 
plug  connected  to  a  flexible  cord  into  a  pin-jack  which  is  connected  in  series 
with  the  line  upon  which  the  calling  office  is  located.  The  flexible  cord 
in  turn  being  connected  with  a  common  operating  set — in  this  case  a  Morse 
relay,  sounder  and  key. 

Figure  315  shows  a  method  in  use  at  some  offices.  If  the  circuits  are  care- 
fully traced  it  will  be  seen  that  when  the  branch-office  operator  desires  to 
attract  the  attention  of  the  main-office  attendant,  the  only  action  necessary 
is  to  momentarily  open  the  branch-office  key.  This  results  in  the  armature 
lever  of  the  2o-ohm  pony  relay  making  connection  with  its  back-stop  long 
enough  to  permit  current  from  the  local  dynamo  to  actuate  the  annunciator, 
the  shutter  of  which  falls  and  closes  the  lamp  circuit,  the  lamp  remaining 
lighted  until  the  shutter  is  restored  to  the  normal  position  by  the  main-office 
attendant.  The  latter  then  inserts  the  plug  in  the  closed-circuit  jack,  thereby 
connecting  the  i5o-ohm  instrument  into  the  circuit,  enabling  the  branch 
office  to  transact  business  in  the  usual  manner.  After  the  message  has  been 
received  the  main-office  attendant  withdraws  the  plug  and  inserts  it  in  the 
closed-circuit  pin-jack  of  another  similar  circuit,  the  annunciator  of  which 
has  in  the  meantime  signalled  a  call  from  another  office. 

The  number  of  circuits  which  may  be  satisfactorily  attended  to  by  one 
operator  depends  upon  the  ability  of  the  operator,  and  upon  the  frequency 
of  calls  upon  the  various  circuits.  In  some  instances  one  operator  can  safely 
handle  a  dozen  or  more  circuits,  while  in  other  cases  one  or  two  circuits 
will  keep  one  man  busy.  One  great  advnatage  derived  from  this  arrange- 
ment is  that  an  operator  can  attend  to  a  number  of  circuits  without  having 
to  move  around  from  table  to  table  as  was  necessary  in  the  city  line  and 
way-wire  departments  before  the  annunciator  systems  were  introduced. 

THE  NEEDHAM  ANNUNCIATOR 

A  very  satisfactory  annunciator,  the  invention  of  Mr.  J.  T.  Needham, 
and  used  extensively  by  the  Postal  Telegraph-Cable  Company,  is  illustrated 
in  Fig.  316,  which  shows  both  main-office  and  branch-office  wiring.  At 
the  main  office  the  annunciator  is  connected  directly  in  the  line — no  pony 
relay  being  required.  The  annunciator  is  mounted  in  the  center  of  the 
operating  table,  and  has  one  closed-circuit  pin-jack  facing  each  side  of  the 
table  so  that  the  call  may  be  answered  from  either  side.  Opening  the  key 
at  the  branch  office  results  in  demagnetization  of  the  annunciator  magnet, 
permitting  a  spring  attached  to  the  armature  to  move  the  "semaphore" 
into  the  signaling  position.  Insertion  of  the  double  plug  of  the  Morse  set 


BRA  NCH-OFFICE  A  NN  UN  CIA  TORS 


361 


into  either  pin- jack  mechanically  restores  the  semaphore  to  the  non-signaling 
position.  As  usually  arranged,  the  semaphore  in  turning  causes  a  local 
circuit  to  close,  which  lights  an  incandescent  lamp,  and,  as  the  lamp  remains 
lighted  until  the  plug  attached  to  the  flexible  conductors  of  the  Morse  set 
is  inserted  in  the  annunciator  pin- jack,  the  number  of  lights  burning  at 
one  time  in  any  division  constitute  an  unquestionable  indication  of  the 
number  of  unanswered  calls. 

y 

BRANCH 


9p6 


FIG.  316. — The  Needham  annunciator  for  concentrated  circuits. 


OFFICE  SIGNALING  ARRANGEMENTS  FOR  DUPLEX  AND   QUADRUPLEX 

CIRCUITS 

At  the  present  time  it  is  the  usual  practice  to  concentrate  all  duplex 
and  quadruplex  equipment  in  a  department,  removed  to  a  greater  or  less 
distance  from  the  tables  at  which  the  operators  sit  while  sending  or  receiving 
messages;  the  connections  between  the  multiplex  sets  and  the  operating 
tables  being  made  through  the  loopswitch  as  previously  explained.  An 
operator  working  on  a  quadrulpex  circuit  may  be  located  at  a  table  situated 
100  ft.  or  more;  distant  from  the  quadruplex  apparatus  proper.  When 
trouble  of  any  kind  develops  in  the  operation  of  the  circuit,  it  is  necessary 
that  the  operator  have  at  hand  a  means  of  signaling  to  the  quadruplex 
attendant  for  attention. 

The  arrangement  used  for  this  purpose  by  the  Postal  Company  is  depicted 
theoretically  in  Fig.  317.  The  annunciator  mounted  on  a  shelf  or  table  as  a 
component  part  of  each  duplex  and  quadruplex  set,  is  connected  in  series 
with  the  pole-changer  magnet  winding"  as  shown  in  the  diagram.  The 
ampere-turns  of  the  winding  of  the  annunciator  magnet  are  of  such  value 
that  the  normal  current  strength  obtaining  in  the  circuit  is  not  sufficient 


362 


AMERICAN  TELEGRAPH  PRACTICE 


to  cause  the  armature  of  the  annunciator  to  be  attracted.  When,  however, 
the  operator  depresses  the  push-button  it  is  evident  that  the  current  strength 
will  be  raised  considerably,  as  now  a  5o-ohm  path  to  ground  has  been  sub- 


Lamp 


FIG.  317. — Signaling  arrangement  between  operating  table  and  multiplex  department. 


Q 

10 

D 

DO 

FIG.  318. — Form  of  multiplex  annunciator. 

stituted  in  place  of  the  i5o-ohm  path  to  ground  via  the  2o-ohm  sounder  and 
the  i3o-ohm  resistance  coil  at  the  loopswitch.  Obviously,  the  retractile 
spring  attached  to  the  armature  of  the  annunciator  must  be  adjusted  so  that 
the  normal  current  used  to  operate  the  pole-changer  will  not  actuate  the 


BRANCH-OFFICE  ANNUNCIATORS  363 

annunciator.     The  arrangement  here  considered  is  quite  similar  to  that  de- 
scribed in  connection  with  Fig.  312. 

Figure  318  illustrates  the  actual  appearance  of  this  type  of  lamp  annunci- 
ator.    Two  units  are  shown  mounted  side  by  side. 


WESTERN  UNION  SIGNALING  SYSTEM  FOR  DUPLEX  AND  QUADRUPLEX 

CIRCUITS 

In  principle  this  system  is  the  same  as  that  previously  described,  but 
certain  accessory  devices  are  added  which  change  somewhat  the  appearance 
of  the  apparatus. 

Figure  319  shows  the  circuit  arrangements  where  the  system  is  used  for 
branch  office  signaling  on  duplex  or  quadruplex  circuits,  also  when  used  for 
signaling  purposes  between  operating  tables  and  the  quadruplex  department 
of  main  operating-rooms. 

Pressing  a  button  at  the  distant  operating  table  causes  a  lamp  to  be 
lighted  at  the  quadruplex  set.  In  case  the  circuit  is  in  need  of  attention 
from  the  wire  chief  or  the  quadruplex  attendant,  the  operator  presses  the 
button  thereby  causing  both  a  visible  and  an  audible  signal  to  be  registered 
at  the  quadruplex  table.  If  the  circuit  is  not  completely  interrupted,  opera- 
tion may  be  continued,  as  the  light  will  not  be  extinguished  until  the  attend- 
ant answers  at  the  multiplex  set.  At  the  instant  the  attendant  opens  his 
key  in  order  to  learn  the  occasion  for  the  signal,  the  light  is  automatically 
extinguished.  When  the  circuit  has  been  made  good  and  the  key  at  the 
quadruplex  set  closed,  the  lamp  is  again  ready  to  respond  to  subsequent 
signals  from  the  operator  working  the  circuit. 

The  operation  of  this  arrangement  is  dependent  upon  a  i-ohm  "pony" 
relay  of  special  design.  Where  "loops"  or  "legs"  are  directly  connected 
to  a  duplex  or  to  one  side  of  a  quadruplex,  one  of  these  relays  is  connected 
in  the  pole-changer,  or  transmitter  local  circuit.  The  relay  is  not  actuated 
by  the  regular  current  of  about  250  milliamperes,  but  its  armature  is  attracted 
when  the  current  is  raised  to  a  strength  of  350  milliamperes,  which  strength 
obtains  when  the  push-button  at  the  operating  table  is  depressed.  When  an 
operating-room  loop  is  connected  to  the  set  the  increase  of  current  strength 
is  accomplished  by  presenting  a  path  to  ground  via  the  push-button,  which 
has  a  considerably  lower  resistance  than  that  of  the  regular  circuit  via  the 
8o-ohm  lamp. 

In  order  to  operate  the  signal  from  a  branch  office  or  a  broker's  office,  a 
3-point  push-button  is  employed,  which  applies  an  additional  battery  for 
the  purpose  of  momentarily  increasing  the  value  of  the  current  flowing  in 
the  circuit.  The  increased  current  strength  is  sufficient  to  cause  the  signal 
relay  to  attract  its  armature,  and  this  in  turn  closes  the  lamp  circuit.  It 
will  be  seen  that  while  the  armature  of  the  signal  relay  is  in  the  closed  position 


364 


AMERICAN  TELEGRAPH  PRACTICE 


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AMERICAN  TELEGRAPH  PRACTICE 


it  will  remain  there  as  long  as  the  key  at  the  quadruplex  set  remains  closed, 
as,  now,  the  350  milliamperes'  current  flowing  through  the  lamp  circuit  (from 
the  26-volt  dynamo)  also  traverses  the  winding  of  the  signal  relay,  and,  being 
of  the  required  strength,  holds  the  armature  in  the  closed  position.  The 
lamp,  therefore,  remains  lighted  until  the  quadruplex  attendant  comes  to  the 
set  and  opens  his  key  in  trie  act  of  communicating  by  Morse  with  the  operator 
working  the  circuit,  for  the  purpose  of  learning  the  nature  of  the  difficulty. 
At  the  instant  the  key  is  opened  the  circuit  from  the  26-volt  dynamo  is  inter- 
rupted, resulting  in  the  release  of  the  armature  of  the  signal  relay,  which  in 
turn  opens  the  lamp  circuit  and  causes  the  light  to  be  extinguished. 

Figure  320  shows  the  signaling  circuits  as  arranged  when  sending  and 
receiving  legs  are  connected  to  the  multiplex  set  through  a  double-loop 
repeater.  In  this  case  the  repeater  apparatus  includes  one  of  the  special 
relays  which  repeats  into  the  multiplex  sending  circuit  the  signal  produced 
by  pressing  the  push-button  in  the  sending  leg  connected  through  the  double- 
loop  repeater. 

MAIN-LINE  CALL  BELLS,  USING  SECOND  SIDE  OF  QUADRUPLEX 

In  order  to  expedite  circuit  changes  at  terminal  offices,  it  is  quite  often 
advisable  to  maintain  "bell"  wires  between  the  terminal  offices  of  the  various 


JoLeqBoard 


FIG.  321. — Main-line  call  bell,  second  side  of  quadruplex.     Opening  the"B"  side  key  at 
the  distant  station  operates  the  annunciator. 

wire  districts  so  that  wire  chiefs  may  have  an  ever  ready  means  of  communi- 
cating with  each  other  without  being  required  to  send  service  messages  over 
wires  carrying  regular  traffic,  or  without  having  to  set  up  a  special  circuit 
for  the  purpose  on  each  occasion  that  such  communication  is  necessary. 


MAIN -LINE  CALL  BELLS 


367 


To  maintain  such  communication  between  the  various  terminal  offices 
it  is  the  usual  practice  to  "quad"  circuits  over  which  duplex  service  only 
is  to  be  maintained,  in  which  case  the  polar  side  is  assigned  to  carry  regular 
traffic,  while  the  neutral  side  is  used  for  bell-wire  purposes.  At  Chicago,  for 
instance,  the  eastern  wire  chief  may  have  a  bell  wire  to  Detroit,  Cleveland, 
Indianapolis,  Columbus,  etc.,  or  to  each  terminal  office  with  which  he  makes 
wire  changes,  where  quadruplex  equipment  is  available  for  the  purpose. 

Figure  ,321  shows  theoretically  the  local  circuit  arrangements  necessary 
for  the  operation  of  the  bell  and  lamp.  The  polar  side  of  the  quadruplex 
used  is  operated  from  the  long-end  potentials  at  each  end  of  the  circuit, 
that  is,  the  neutral  side  keys  at  each  station  are  normally  closed,  which  pro- 
vides that  the  neutral  relays  and  bug-trap  relays  also,  at  each  end  will 
remain  closed  normally.  The  diagram  shows  the  bug-trap  connections  of 
the  quadruplex  set  at  one  station  only.  To  operate  the  signal,  the  only 


R.5. 


To  Leg  Board 


FIG.  322. — Main-line  call  bell,  second  side  of  quadruplex.     Closing  the  "B"  side  key  at 
the  distant  station  operates  the  ammciator. 


action  necessary  on  the  part  of  the  wire  chief  at  the  distant  station  is  to  open 
the  transmitting  key  on  the  neutral  side,  thereby  placing  the  short-end 
battery  to  line.  This  results  in  the  armature  tongue  of  the  pony  relay  making 
contact  with  its. back-stop,  permitting  current  from  the  local  battery  to 
energize  the  annunciator  magnet  which  raises  the  indicator  into  view,  at  the 
same  time  closing  the  lamp  and  bell  circuit.  The  wire  chief  at  the  station 
called,  in  responding,  holds  the  center  lever  of  the  cam  switch  to  the  left  so 
that  the  annunciator  will  remain  silent  while  the  conversation  continues. 
The  call  is  answered  by  means  of  a  key  which  controls  the  operation  of  the 
transmitter  of  the  quadruplex  set,  and  the  conversation  is  carried  on  in  the 


368 


AMERICAN  TELEGRAPH  PRACTICE 


usual  manner — by  Morse-^over  the  neutral  side  without  interfering  with  the 
traffic  being  handled  on  the  polar  side  of  the  quadruplex. 

When  the  conversation  is  over,  the  center  lever  of  the  cam  switch  is  re- 
leased and  returns  to  the  position  shown  in  the  diagram,  again  placing  the 
annunciator  in  circuit  with  the  back  contact  point  of  the  pony  relay. 

In  practice  the  annunciator,  lamp,  bell,  relay,  sounder,  cam  switch  and 
Morse  key  are  conveniently  mounted  at  the  main  switchboard,  and  by 
means  of  loopswitch  connections,  the  neutral  side  of  any  quadruplex  set 
may  be  connected  thereto,  so  that  the  wire  chief — without  leaving  his  post — 
may  signal  to  the  switchboard  attendant  at  any  distant  terminal  office  with 
which  bell-wire  service  is  maintained. 


To  Leg  Board 


FIG.  323. — Main-line  call  bell  for  "short-end"  signaling. 

On  short  quadruplex  circuits,  where,  ordinarily,  the  short-end  current 
strength  is  sufficient  to  satisfactorily  operate  the  polar  side,  the  bell-wire 
annunciator  may  be  operated  by  temporarily  applying  the  long-end  potential 
to  the  line.  Fig.  322  shows  the  receiving  loop  connections  where  long-end 
signaling  is  maintained. 

Figure  323,  shows  the  necessary  connections  in  those  installations  where 
the  receiving  side  is  extended  from  the  quadruplex  set  to  the  wire  chief's 
desk  by  means  of  a  loop,  the  local  circuits  being  arranged  for  short-end 
signaling. 

It  will  be  noted  that  the  lamp  does  not  remain  lighted  until  the  call  is 
answered  unless  the  signaling  key  at  the  distant  station  is  left  open,  leaving 
the  short-end  battery  in  contact  with  the  line.  The  signal,  therefore,,  may  be 
made  intermittent  or  continuous  as  desired. 

MAIN-LINE  "SELECTOR"  SIGNALING 

Consider  an  important  circuit  made  up  as  depicted  in  Fig.  324,  extending 
from  a  branch  office  in  New  York  City  to  a  branch  office  in  Kansas  City,  all 


SELECTOR  SIGNALING  369 

stations,  excepting  the  two  branch  offices,  having  repeaters  in  the  circuit. 
If  delays  due  to  wire  trouble  or  to  repeater  defects  are  to  be  kept  down  to  the 
lowest  possible  duration,  it  is  necessary  either  to  maintain  a  rider  at  each 
repeater,  or  to  provide  the  branch  office  at  each  terminal  with  a  means  of 
"ringing  in"  any  one  or  all  of  the  repeater  offices  when  trouble  develops. 

Selectors  have  been  used  on  various  railroads  throughout  the  country 
during  the  past  20  years  to  afford  train  dispatchers  a  means  of  sounding  a 
bell  alarm  at  stations  where  but  one  operator  is  employed,  and  whose  duties 
at  times  take  him  out  of  hearing  of  the  regular  Morse  instrument.  The 

New  York  Pitfsburg  Chicago  Kansas  City 

Branch 


8 ft 


—  ~    •=• 
FIG.  324. — Long  circuit  connected  through  four  repeaters. 

selector  at  each  station  along  the  line  responds  to  a  particular  combination 
of  dashes  made  with  the  Morse  key,  or  by  a  specially  constructed  call  box, 
similar  to  the  call  boxes  used  as  messenger  calls  in  district  messenger  systems, 
the  selector,  of  course,  being  entirely  unresponsive  to  the  opening  and  closing 
of  the  main-line  circuit  when  Morse  signals  are  being  transmitted. 

Within  recent  years  selectors  have  been  developed  which  may  be  used  on 
metallic-circuit  telephone  train-dispatching  circuits,  without  interfering  with 
telephonic  conversation,  and  without  introducing  appreciable  transmission 
losses,  but  for  the  purposes  of  the  present  work  it  will  be  sufficient  to  consider 
only  the  connections  necessary  in  applying  the  selector  to  circuits  operated 
as  single  Morse  lines,  and  as  duplexed  lines. 

THE  GILL  SELECTOR 

The  main  features  of  the  Gill  selector  are  a  combination  wheel  and  a 
time  wheel  which  is  normally  held  at  the  top  of  an  inclined  track.  The 
operation  of  the  selector  magnet  allows  the  time  wheel  to  roll  down  the  track. 
If  the  magnet  is  operated  rapidly  the  wheel  does  not  get  to  the  end  of  its 
travel  before  being  pushed  back  again.  A  small  pin  in  the  side  of  a  pawl 
engaging  the  combination  wheel  normally  opposes  the  combination  wheel 
teeth  near  their  outer  points.  When  the  time  wheel  falls  to  the  bottom  of 
the  track,  however,  the  pawl  is  allowed  to  drop  to  the  bottom  of  the  tooth. 
Some  of  the  teeth  on  the  combination  wheel  are  so  formed  that  they  will 
effectually  engage  with  the  pawl  only  when  the  latter  is  in  its  normal  position, 
while  others  will  engage  only  when  the  pawl  is  at  the  bottom  position.  Thus 
innumerable  permutations  may  be  made,  which  will  respond  to  certain  com- 
binations of  rapid  electric  impulses  with  intervals  between.  The  correct 

24 


370 


AMERICAN  TELEGRAPH  PRACTICE 


FIG.  325.— The  Gill  selector. 


FIG.  326. — Call-box  to  operate  Gill  selector. 


SELECTOR  CIRCUITS 


371 


sequence  of  impulses  and  intervals  steps  the  combination  wheel  around,  so 
that  a  contact  is  made.  All  other  wheels  fail  to  reach  the  contact  position 
because  at  some  point  or  points  in  their  revolution  the  pawl  has  slipped  out, 
allowing  the  combination  wheel  to  return  to  its  initial  position. 

Figure  325  shows  a  view  of  the  Gill  selector.  The  mechanism  is  enclosed 
in  a  glass  case,  mounted  on  a  porcelain  base  with  the  combination  number  to 
which  the  selector  responds  marked  thereon. 

Figure  326  shows  a  view  of  the  call  box  (cover  removed)  which  is  connected 
around  the  Morse  key,  the  combination  number  of  the  box  being  stamped  on 
the  handle.  In  order  to  transmit  the  combination  over  the 'line  all  that  is 
necessary  is  to  give  the  handle  a  quarter  turn  and  release  it. 


1.500 


FIG.  327. — Gill  selector  connected  into  a  duplexed  circuit,  where  no- volt  local  current 

is  used. 

When  the  main-line  windings  of  the  selector  have  been  actuated  by  the 
correct  combination  of  impulses  the  local  secondary  circuit  is  closed  for  a 
moment  or  two,  and,  where  the  secondary  circuit  includes  directly  a  battery 
and  a  vibrating  bell,  the  hammer  of  the  bell  will  tap  the  gong  but  a  few  times 
on  each  occasion  that  the  signal  combination  to  which  that  particular  selector 
responds  is  transmitted  over  the  line.  If  the  signal  is  to  be  continuous  until 
answered  it  is  necessary  that  the  local  circuit  of  the  selector  proper  shall  in 
turn  operate  an  annunciator  which  will  close  a  bell  or  lamp  circuit  as  shown 
in  Fig.  327.  In  such  cases,  where  auxiliary  annunciators  are  provided,  the 
bell  continues  to  ring,  or  the  lamp  continues  to  burn  until  the  "drop"  of 
the  annunciator  is  reset  in  the  vertical  position. 

Figure  328  shows  the  wiring  of  the  selector  equipment  in  use  where  40- 
volt  local  current  is  employed.  The  main-line  coils  of  the  selector  are 
connected  to  a  cord  and  wedge  so  that  the  selector  may  be  connected  into 
the  receiving  side  of  any  duplex  or  quadruplex  set  at  the  leg-board  as  indicated 
in  the  diagram.  In  practice,  of  course,  the  selector  and  annunciator  are 
mounted  on  the  same  table  or  shelf  as  the  multiplex  equipment,  and  the  two 


372 


AMERICAN  TELEGRAPH  PRACTICE 


wires  from  the  selector  main-line  binding-posts  terminate  in  a  pin-jack 
located  in  the  pin-jack  panel  of  the  leg-board,  the  connection  being  made 
with  the  spring- jack  by  means  of  a  flrxible  cord  equipped  at  one  end  with  a 
double  plug  and  at  the  other  end  with  a  double  wedge. 


FIG.  328.— Gill  selector  connected  into  a  duplexed  circuit,  where  40- volt  local  current  is 

used. 


FIG.  329.— Gill  selector  connected  into  a  single  Morse  line,     no- volt  local  battery. 

The  annunciator  arrangement  illustrated  in  Fig.  328  has  a  locking  magnet 
controlling  the  operation  of  the  armature  which,  when  in  the  closed  position, 
maintains  the  battery  circuit  through  the  lamp  circuit  intact  after  the  local 


SELECTOR  CIRCUITS 


373 


FIG.  330. — Gill  selector  connected  into  a  single  Morse  line  at  a  way  office  using  gravity 

battery  locals. 


FIG.  331. — Gill  selector  and  lamp  annunciator. 


•HI- 

irav/ty 
lattery 


00 


Relay 


Bel  I  Annunciator 

FIG.  332. — Selector  connected  to  single-line  repeater.     Gravity  battery  locals. 


374 


AMERICAN  TELEGRAPH  PRACTICE 


contacts  of  the  selector  have  separated.  To  silence  the  bell  and  reset  the 
annunciator  it  is  necessary  only  to  depress  the  key  momentarily,  thus 
breaking  the  circuit  to  ground.  This  causes  the  loo-ohm  magnet  to  release 
its  armature,  so  that  when  the  key  is  released,  the  bell  circuit  will  remain 
open  until  the  selector  local  contacts  are  again  closed  in  response  to  the 
operation  of  the  selector. 

Figure  329  shows  the  connections  necessary  where  the  selector  is  con- 
nected into  a  single  Morse  line;  the  operation  of  the  selector  controlling 
a  bell  annunciator. 


Lamp  Annunciator  A/a  IL 
Use  40V.  Lamp 


FIG.  333. — Selector  connected  to  single-line  repeater.     40- volt  local  battery. 

Figure  330  shows  the  connections  of  a  selector,  annunciator,  and  bell 
combination  at  a  way  office,  or  on  a  single  wire  where  gravity  battery  locals 
are  used. 

Figure  331  is  the  same  as  the  arrangement  shown  in  Fig.  328  except 
that  the  selector  operates  a  bell  annunciator  instead  of  a  lamp  annunciator. 

Figure  332  shows  the  connections  required  where  the  selector,  annunci- 
ator, and  bell  equipment  is  used  in  connection  with  a  single-line  repeater  at  a 
repeater  station,  the  annunciator  and  bell  being  operated  by  an  extra  battery 
consisting  of  two  gravity  cells. 

Figure  333  shows  the  repeater-station  connections  where  4o-volt  battery 
is  available  for  the  operation  of  local  circuits. 


i 


CHAPTER  XVIII 

HALF-SET  REPEATERS.  COMBINATION  FULL-SET  AND  HALF- 
SET  REPEATERS.  "HOUSE"  REPEATER  CIRCUITS.  DUPLEX 
AND  QUADRUPLEX  REPEATERS.  DIRECT-POINT  REPEATERS. 
LEASED  WIRE  INTERMEDIATE  "DROPS" 

A  " half-set"  repeater,  consisting  of  one  repeater  transmitter  and  one 
repeater  relay,  is  used  where  it  is  desired  to  connect  a  duplexed  line  or  one 
side  of  a  quadruplexed  line  with  a  single  line.  When  such  connection  is 
made  the  duplexed  portion  of  the  circuit  is  used  for  transmission  in  one 
direction  at  a  time  only.  The  capacity  of  the  entire  circuit,  therefore,  is 
simply  that  of  a  single  Morse  circuit. 

A  wire  may  be  quadruplexed 
between  stations  A  and  B,  Fig. 
334,  and  by  employing  two  sepa- 
rate half-set  repeaters,  two  branch 
lines  operated  as  single  Morse  cir- 
cuits between  B  and  C  and  between 

B  and  D  may  be  connected  with  _ 

....  FIG.  334. — Two    single    lines    connected    to   a 

the  quadruplexed  wire  so  that  A  quadruplexed  line, 

will    have    direct  communication 

with  C,  on,  say,  the  polar  side  of  the  quadruplex,  and  with  D  on  the  neutral 
side  of  the  quadruplex,  and  while  transmission  can  take  place  in  one  direc- 
tion only,  at  a  time,  over  each  half  of  the  quadruplex,  the  arrangement  pro- 
vides that  one  wire  between  stations  A  and  B  will  serve  the  purpose  of  two 
wires. 

Figure  335  shows  the  main-line  and  local  connections  at  a  "Postal" 
terminal  office  where  a  single  wire  is  connected  into  the  polar  side  of  a 
quadruplex,  or  a  polar  duplex.  Line  No.  i  entering  the  office  is  connected 
with  the  shoe  of  a  spring-jack  at  the  main-line  switchboard,  thence  through 
one  conductor  of  a  double  cord  to  the  relay  of  a  Weiny  half-set  repeater, 
returning  via  the  tongue  of  the  repeater  transmitter,  the  other  conductor 
of  the  double  cord,  the  shank  of  the  spring- jack,  thence  via  the  vertical  brass 
strap  of  the  switchboard,  metal  plug,  and  disk  to  battery  and  ground. 
Wire  No.  4  connected  with  the  shoe  of  its  spring-jack  is  connected  with  the 
duplex  set  by  means  of  a  single  conductor  cord — the  metal  face  of  the  wedge 
being  in  contact  with  the  shoe  and  the  insulating  face  with  the  shank  of  the 
spring-jack.  The  single  wire  extending  from  the  pin-jack  to  the  duplex  set 

375 


376 


AMERICAN  TELEGRAPH  PRACTICE 


makes  the  usual  connections  through  polar  relay,  artificial  line,  pole-changer 
and  battery.  The  local  circuit  extensions  from  the  polar  relay  and  the  pole- 
changer  to  separate  spring-jacks  in  the  leg-board  provide  by  means  of  a 
double  conductor  cord — connecting  the  polar  relay  spring- jack  with  the  re- 
peater sending  side  pin- jack — that  the  operation  of  the  repeater  transmitter 
will  depend  upon  the  opening  and  closing  of  the  armature  of  the  polar  relay, 
and  by  means  of  a  double  conductor  cord — connecting  the  pole-changer 
spring-jack  with  the  repeater  receiving  side  pin-jack — that  the  operation  of 
the  pole-changer  will  depend  upon  the  opening  and  closing  of  the  armature 
of  the  repeater  relay.  The  operation  of  the  combined  sets  may  readily  be 

I    23  4 


FIG.  335. — Single  line  connected  to  a  duplexed  line  through  a  half  repeater. 

traced,  and  it  will  be  found  that  when  the  key  at  the  office  on  the  single  line 
is  closed,  the  armature  of  the  repeater  relay  will  be  in  the  closed  position, 
also  the  armature  of  the  pole-changer  of  the  duplex  will  be  in  the  closed  posi- 
tion which  provides  that  the  receiving  sounder  circuit  of  the  polar  relay  at  the 
distant  station  on  the  duplexed  line  will  be  closed.  When,  on  the  other  hand 
the  single-line  key  is  open,  the  armature  of  the  repeater  relay  will  be  in  the 
open  position,  the  armature  of  the  pole-changer  of  the  duplex  in  the  open  posi- 
tion, and  the  receiving  sounder  circuit  of  the  duplex  at  the  distant  station 
will  be  open.  Thus  the  operation  of  the  polar  relay  at  the  distant  station  is 
controlled  by  the  operation  of  the  transmitting  key  at  the  office  on  the  single 
line. 

The  operation  of  the  relay  at  the  station  on  the  single  line  is  controlled 
by  the  operation  of  the  pole-changer  of  the  duplex  at  the  distant  station  on 


HALF-SET  REPEATERS  377 

the  duplexed  line,  by  the  reverse  process,  that  is,  when  the  distant  pole- 
changer  is  closed  the  armature  of  the  polar  relay  at  the  repeater  station  will 
be  in  the  closed  position,  which  in  turn  closes  the  repeater  transmitter  there- 
by applying  battery  to  the  single  line,  causing  the  single  line  relay  to  attract 
its  armature.  When  the  pole-changer  of  the  duplex  at  the  distant  station  is 
"open,"  the  armature  of  the  polar  relay  at  the  repeater  station  will  be  in  the 
open  position,  thereby  breaking  the  local  40-volt  battery  connection  through 
the  windings  of  the  repeater  transmitter,  causing  the  latter  to  release  its 
armature  removing  the  main-line  i3o-volt  battery  from  contact  with  the 
single  line.  Thus  the  operation  of  the  single  line  relay  is  controlled  by  the 
operation  of  the  pole-changer  of  the  duplex  at  the  distant  station. 

When  two  lines  are  connected  in  this  manner,  it  is  necessary  that  the 
pole-changer  key  of  the  duplex  be  kept  closed  while  the  station  on  the  single 
line  is  sending,  otherwise  there  will  be  no  main-line  battery  applied  to  the 
single  line  at  the  repeater  station. 

When  signals  are  being  repeated  from  the  duplexed  into  the  single  line, 
the  repeater  relay  remains  closed  due  to  the  action  of  the  differential  magnet 
mounted  above  the  main-line  magnet,  as  was  explained  in  connection  with 
Figs.  189  and  190. 

Figure  336  shows  the  method  of  connecting  up  a  Weiny-Phillips  half-set 
repeater  to  a  duplex  or  one  side  of  a  quadruplex,  where  gravity  battery 
locals  are  used.  Where  such  sets  are  installed  in  small  offices,  in  some  cases 
the  half-repeater  set  is  mounted  upon  an  operating  table  so  that  it  may  be 
used  as  an  operating  set  at  the  repeater  office  when  desired.  Additional  local 
battery  is  placed  in  the  local  circuits  of  the  half-repeater  to  insure  "solid" 
signaling.  The  connections  between  the  Morse  and  multiplex  sets  are  made 
at  the  loopswitch  by  means  of  wedges  and  plugs  as  shown  in  the  diagram. 

Figure  337  shows  the  circuits  of  a  Weiny  half-repeater  where  40- volt 
local  current  is  used,  employing  the  new  type  of  repeater  instruments  used 
in  the  service  of  the  Postal  Telegraph-Cable  Company.  In  those  instances 
where  no- volt  local  battery  is  used  in  place  of  the  regulation  40  volts,  a 
6oo-ohm  resistance  unit  is  placed  in  series  with  the  2o-ohm  holding  coil  of 
the  relay.  Also,  the  transmitters  and  sounders  are  wound  to  a  resistance  of 
150  ohms  and  have  i,5oo-ohm  resistance  units  in  each  of  these  circuits;  the 
resistance  units  being  placed  next  to  the  fuse  block  instead  of  next  to  the 
ground  connection  as  shown  when  40- volt  battery  is  used. 

Figure  338  shows  the  circuits  of  a  Weiny-Phillips  repeater  arranged  for 
use  either  as  a  full  set  or  as  a  half  set.  Throwing  the  switches  to  the  right 
provdies  for  the  employment  of  the  apparatus  as  a  single-line  repeater,  i.e., 
for  repeating  from  one  single  line  into  another,  while  throwing  the  switches 
to  the  left  converts  the  set  into  two  separate  half-repeaters.  Also,  with 
this  arrangement  when  no-volt  local  battery  is  employed,  6oo-ohm  and 
i,5oo-ohm  resistance  coils  are  used  as  explained  in  connection  with  Fig.  337, 


378 


AMERICAN  TELEGRAPH  PRACTICE 


HALF-SET  REPEATERS 


379 


ps 

fc 


380 


AMERICAN  TELEGRAPH  PRACTICE 


HALF-SET  REPEATERS 


381 


Figure  339  shows  the  theoretical  connections  of  a  half-set  Milliken 
repeater,  from  which  it  will  be  seen  that  the  principle  of  operation  is  the 
same  as  that  of  the  Weiny  half  set,  and  it  might  here  be  stated  that  any  of 
the  types  of  repeater  described  in  the  chapter  dealing  with  single-line  repeaters 
may  be  employed  as  half  repeaters  simply  by  using  one-half  of  the  apparatus 
required  for  a  full  set. 


Line 


FIG.  339. — Milliken  half  repeater.     Theory. 


To  Quctd.orDup/exSel-  21  Volts 


Relay 

\          •   f  1 

—4 

Key  ' 
\ 

•t 

Cord  forSlnqleLine 


FIG.  340. — Instrument  binding-post  connections  of  the  Milliken  half  repeater. 

Figure  340  shows  the  actual  binding-post  connections  of  a  Milliken 
half-repeater,  the  switchboard  extensions  being  those  used  in  the  service 
of  the  Western  Union  Company. 

Figure  341  shows  the  circuit  arrangements  of  a  house,  or  office  repeater, 
which  by  means  of  a  "double-flip"  connection  at  the  main  switchboard 


382 


AMERICAN  TELEGRAPH  PRACTICE 


provides  for  the  extension  of  the  circuit  to  a  branch  office  at  the  repeater 
station  in  such  manner  that  the  operation  of  the  relay  at  the  branch  office 


EAST  REPEATER  SET 

0000069     0000009 


HOUSE  CIRCUTT /IRRANOEMENT 


OOOOQO 


HALF  REPEATER  SET 


WEST  REPEATER  SET 


ooooo(5p 


FIG.  341. — House-circuit  repeater. 


OOOOOC 


Relay  of  Half  Set 
H 

CD 


i  r 

Branch  Office 

'JayofEastu 
H 

'el- 

hH 

d 

[j       |  One  fa 

1  1 


FIG.  342. — Theory  of  the  house-circuit  repeater. 

will  be  more  reliable  and  regular  than  when  the  branch  office  is  simply 
looped  in  on  the  main  line  on  one  side  of  the  single  repeater.     Fig.  342  shows 


DUPLEX  AND  QUADRUPLEX  REPEATERS 


383 


a  theoretical  diagram  of  the  circuits  as  they  stand  when  the  switchboard 
connections  have  been  properly  made,  and  from  which  the  operation  of  the 
combined  sets  may  easily  be  traced.  This  arrangement  is  in  use  on  the  lines 
of  the  Postal  Telegraph-Cable  Company. 

DUPLEX  AND  QUADRUPLEX  REPEATERS 

Notwithstanding  the  apparent  complexity  of  multiplex  telegraph  appa- 
ratus, the  arrangement  of  such  apparatus  for  the  purpose  of  repeating 
signals  from  one  duplexed  or  quadruplexed  circuit  to  another  line  similarly 
operated,  is  a  comparatively  simple  matter.  All  that  is  required  is  that 
the  electromagnet  which  actuates  the  transmitter  or  pole-changer  of  a 
particular  circuit  be  included  in  the  same  local  circuit  with  the  contact 
points  of  the  receiving  relay  connected  into  another  line.  By  means  of 
loopswitch,  or  leg-board  connections  the  opening  and  closing  of  the  armature 
of  the  neutral  relay  or  the  polar  relay  of  one  quadruplex  set  may  be  made  to 
operate  the  transmitter  or  the  pole-changer  of  another  quadruplex  set. 
When  signals  are  automatically  passed  through  repeater  stations  by  inter- 
connecting the  local  circuits  of  separate  quadruplex  sets,  the  arrangement 
of  circuits  is  termed  a  simple  quadruplex  repeater. 


DIRECT-POINT  DUPLEX  REPEATERS 

With  a  view  to  eliminating  one  pair  of  points  through  which  the  signals 
must  pass  in  being  repeated  from  one  line  to  another,  the  direct-point,  or 
direct-repeating    polar   duplex 
has  been  introduced  in  the  ser- 
vice both  of  the  Postal  Tele- 
graph-Cable Company,  and  the      West 
Western  Union  Telegraph  Com- 
pany.    With  this  arrangement 
the  respective  armature  levers 
of  two  polar  relays  at  the  re- 
peater office  connect  the  posi-  ^ 

.  -.  .     ,  FlG-  343-—   Postal"  direct-point  duplex  repeater, 

tive  and  negative  mam  battery  Theory 

potentials   directly  to  the  line 

wires.  The  principle  upon  which  the  system  operates  will  be  understood 
by  referring  to  the  theoretical  diagram,  Fig.  343.  Assume,  for  instance, 
that  the  distant  eastern  office  has  closed  the  key.  The  armature  of  the 
polar  relay  at  the  repeater  station  will  be  attracted  into  the  position 
shown  in  the  diagram — the  closed  position.  This  results  in  placing  the 
duplex  negative  battery  in  contact  with  the  line  west.  As  the  current 
passes  differentially  through  [the  coils  of  the  polar  relay,  the  armature 


384 


AMERICAN  TELEGRAPH  PRACTICE 


lever  of  the  west  relay  will  not  be  affected  by  the  out-going  impulse.  At 
the  instant  the  key  at  the  distant  eastern  office  is  opened,  the  oppo- 
site battery  pole  is  presented  to  the  line,  which  results  in  the  armature 
lever  of  the  relay  at  the  repeater  station  moving  into  contact  with  the 
positive  battery  terminal,  causing  a  reversal  of  current  in  the  line  west. 
It  will  be  noted  that  each  line  is  grounded  at  the  repeater  station  in  the 
same  manner  that  any  duplexed  line  is  grounded. 

Figure  344  shows  the  connections  of  the  direct  point  repeater  used  by  the 
"  Postal "  company.  The  arrangement  illustrated  is  that  employed  where  the 
connections  between  separate  duplex  sets  are  made  at  the  leg-board.  The 


FIG.  344. — Instrument,  table  switch,  and  leg  board  connections  of  the  Postal  direct- 
point  repeater. 

eastern  wire,  connected  through  the  main-line  side  of  the  polar  relay,  is 
brought  to  the  switch  which  is  the  dividing  point  between  the  main  and 
artificial  lines.  From  there  the  circuit  extends  by  way  of  the  leg-board,  to 
the  armature  tongue  of  the  west  polar  relay,  which,  in  making  connection 
with  its  open  and  closed  contact  points  introduces  either  a  positive  or  negative 
current  for  the  operation  of  the  eastern  circuit,  so  that,  when  the  western 
relay  is  being  operated  due  to  main-line  battery  reversals  at  the  distant  west- 
ern station,  it  causes  reversals  of  main-line  current  to  be  directly  commu- 


DIRECT-POINT  REPEATER 


385 


nicated  through  its  armature  lever  to  the  eastern  circuit,  which,  being 
duplexed,  the  eastern  polar  relay  at  the  repeater  station  is  uninfluenced  thereby, 
and  likewise  the  operation  of  the  western  line  is  directly  dependent  upon  the 
movements  of  the  tongue  of  the  east  polar  relay  at  the  repeater  station. 

When  the  lever  of  the  ground  switch  is  moved  into  connection  with 
the  3oo-ohm  " ground"  coil,  the  circuit  is  grounded  through  a  resistance 
which  equals  that  of  the  dynamos  and  the  internal  resistance  coils.  This 
switch  is  used  in  the  operation  of  balancing. 


FIG.  345. — Binding-post  connections. 

Connected  to  the  tongues  of  the  east  and  west  relays  at  the  repeater  sta- 
tion, are  auxiliary  artificial  circuits  extending  through  2o,ooo-ohm  coils  to 
extra  polar  relays  (the  coils  of  which  are  connected  for  series  operation) 
which  are  used  to  operate  reading  sounders  at  the  repeater  station.  It  is 
evident  that  as  the  local  contact  points  of  the  main-line  relays  are,  in  this 
system,  used  to  make  main-line  battery  applications,  the  points  are  not 
available  for  the  operation  of  reading  sounders  as  is  the  case  with  the  ordinary 
duplex.  The  2o,ooo-ohm  circuit  is  referred  to  as  the  "leak"  relay  circuit, 
and  although  the  strength  of  the  current  traversing  the  windings  of  the  leak 
relay  is  quite  small,  it  is  found  that  when  the  relay  is  properly  adjusted  the 
current  reversals  taking  place  in  the  main  line,  result 'in  clearly  reproduced 
signals  in  the  sounder  operated  by  the  leak  relay. 

Figure  345  shows  the  actual  binding-post   connections  of  a  "Postal" 

25 


386 


AMERICAN  TELEGRAPH  PRACTICE 


direct-point  repeater  set,  the  two  duplex  sets  being  wired  together  so  that  it 
is  not  necessary  to  interconnect  the  sets  at  the  leg-board.  In  the  same  man- 
ner it  is  possible  to  connect  the  polar  sides  of  two  quadruplex  sets  together  in 
order  that  they  may  be  used  as  a  direct  repeater. 


FIG.  346. — Barclay  direct-point  duplex  repeater. 

Figure  346  shows  a  diagram  of  the  wiring  of  the  direct-point  repeater 
used  in  the  service  of  the  Western  Union  Company,  from  which  it  will  be  seen 

that  the  principle  of  operation  is  identical  with 
that  of  the  Postal's  direct  repeater.  In  fact, 
the  only  difference  in  the  two  systems  is  in  the 
method  availed  of  to  provide  a  reading  sounder 
circuit.  For  this  purpose  the  Postal  Company 
employs  a  leak  relay,  while  the  Western  Union 
Company  employs  the  Barclay  polar  relay  which 
is  equipped  with  a  double-lever  armature.  The 

armature  of  the  main-line  relay  has  fixed  to  it 
Armature  „.       ,          ,. 

two  contact  levers,  one  controlling  the  applica- 
tion of  the  duplex  potentials,  while  the  other; 

moving  in  unison  therewith,  closes  and  opens  a  local  sounder  circuit  in  the 
same  way  that  the  lever  of  an  ordinary  polar  relay  operates  its  reading 
sounder  circuit. 


DIRECT-POINT  REPEATER 


387 


Figure  347  shows  a  view  of  the  double-lever  armature  employed  for  the 
purpose;  the  levers,  of  course,  are  insulated  from  each  other. 


BRANCH  OFFICE  CONTROL  OF  DIRECT  POINT  REPEATERS 

Figure  348  is  a  diagram  of  the  circuits  of  a  direct-point  repeater  showing 
branch-office  control  at  the  repeater  station. 

The  local  connections  shown  are  those  of  the  Postal  Telegraph  Company's 
repeater,  but  the  method  Js  applicable,  as  well,  where  the  Barclay  relay  is 
employed.  J 


Branch  jl    Third  key  to  send 

f{4  both  directions 

•ill V   if  desired. 

0    Omit  keys  land  Z 
if  not  needed. 

FIG.  348. — Branch  office  control  of  direct-point  repeater. 

It  will  be  observed  that  the  center  key  at  the  branch  office,  when  closed, 
completes  a  ground  connection,  thereby  combining  the  four  wires  extending 
to  the  branch  office  into  two  grounded  loops,  each  loop  including  trie  polar 
relay  and  pole-changer  local  circuits  of  one  of  the  duplex  sets  forming  the 
repeater.  Key  No.  i  at  the  branch  office  is  used  when  that  office  desires  to 
communicate  with  the  distant  western  office  only.  Key  No.  2  is  used  when 
the  branch  office  desires  to  communicate  with  the  distant  eastern  office  only, 
and  key  No.  3  is  used  when  the  branch  office  wishes  to  transmit  to  the  west 
and  to  the  east  at  the  same  time.  How  this  is  accomplished  is  apparent 
when  it  is  noted  that  at  the  instant  key  No.  3  is  opened,  the  ground  contact 
is  removed  from  the  loops,  and  if  the  local  circuits  are  traced  in  both  direc- 
tions from  the  40- volt  dynamos,  it  will  be  seen  that  the  action  of  one  dynamo . 


388 


AMERICAN  TELEGRAPH  PRACTICE 


is  opposed  by  that  of  the  others,  as  a  consequence  of  which  the  magnets  of 
the  two  sounders  and  two  pole-changers  are  de-energized,  permitting  the 
armature  lever  of  each  instrument  to  move  into  contact  with  its  back-stop 
due  to  the  action  of  its  actuating  spring.  When  the  No.  3  key  is  closed  in 
the  act  of  signaling,  the  ground  connection  is  reestablished  causing  the  four 
armatures  to  respond  and  make  contact  with  their  front-stops. 

A  similar  branch-office  arrangement  is  sometimes  employed  where  simple 
quadruplex  repeaters  are  used.  Fig.  349  shows  the  theoretical  connections 
at  the  main  and  at  the  branch  office  where  this  method  is  used  in  connection 
with  ordinary  quadruplex  repeaters.  In  order  that  the  main  office  may  trans- 
mit in  both  directions  when  called  to  the  circuit,  an  extra  key  controlling  the 
operation  of  an  extra  pole-changer  in  each  duplex  set  is  connected  as  shown 
in  the  diagram. 


FIG.  349.— Branch  office  control  of  simple  quadruplex  repeaters. 

Instead  of  using  two  extra  pole-changers  at  the  main  office  to  enable  the 
attendants  there  to  operate  the  circuit,  the  ground  connection  may  be  ex- 
tended from  the  branch-office  grounding  key,  back  to  the  main  office  as 
indicated  in  Fig.  350. 

The  switching  connections  necessary  at  the  main  office  to  apply  this 
method  of  branch-office  control  to  quadruplex  or  duplex  systems  wired  in  the 
usual  manner,  are  made  by  means  of  cords  and  wedges  at  the  leg-board. 

Figure  351  shows  the  required  leg-board  connections,  where  the  Postal 
Telegraph-Cable  Company's  leg-board  system  is  employed.  The  sending 
and  receiving  local  circuits  of  a  duplex  set,  or  of  the  polar  side  of  a  quadru- 
plex set  are  shown  in  the  upper  portion  of  the  diagram,  while  the  sending 


BRANCH  OFFICE  CONTROL  OF  DUPLEX  REPEATER      389 

and  receiving  local  circuits  shown  in  the  center  portion  of  the  diagram  are 
those  of  the  duplex,  or  polar  side  of  the  quadruplex  connected  therewith  for 
the  purpose  of  repeating  from  one  line  to  another. 


Mam  Office 


West 


Branch 
Office 


FIG.  350. — Center  key  ground  connection  extended  to  main  office. 


Opened 


Main  Office 


Opened 


Branch 


FIG.  351. — Leg  board  cord  connections  providing  branch  office  control  of  duplex  repeater. 

In  addition  to  the  flexible  cord  connections  made  at  the  leg-board  it  is 
necessary  that  the  6-point  " local"  switches  of  set  No.  i  be  thrown  " apart," 
and  that  the  6-point  " local"  switches  of  set  No.  2  be  thrown  "together" 
(see  Figs.  295  to  298  inclusive). 


390 


AMERICAN  TELEGRAPH  PRACTICE 


BRANCH  OFFICE  COMBINATION  SETS 

In  the  interest  of  flexibility  it  is  advisable  to  provide  a  switching  arrange- 
ment at  the  branch  office  by  means  of  which  the  loop  extending  to  the  main 
office  may  be  used  for  either  single  or  duplex  operation.  Fig.  352  shows  the 
connections  necessary  where  a  6-point  switch  is  used  for  this  purpose.  Mov- 
ing the  levers  of  both  switches  to  the  left  provides  for  duplex  service,  while 
moving  the  switch  levers  to  the  extreme  right  provides  for  single-line 
operation. 


Switches  to  Right  Morse  Loop  • 
»     "left-  Duplex  » 

FIG.  352. — Branch  office  combination  set  where  branch  office  controls  the  operation  of 

pole-changer  at  main  office. 


DUPLEX  CONNECTED  WITH  A  BRANCH  OFFICE  OVER  A  SINGLE  CONDUCTOR 

For  emergency  service,  where  the  number  of  conductors  extending  to 
a  branch  office,  convention  hall,  cr  athletic  field  must  be  employed  to  the 
best  advantage,  and  where  it  is  not  convenient  to  use  half-repeaters,  the 
arrangement  depicted  in  Fig.  353  has  been  used  with  excellent  results.  The 
shaded  portions  of  the  wedges  represent  the  metal  faces  in  contact  with  the 
shoe  and  the  shank,  respectively,  of  the  spring- jack,  the  same  being  separated 
electrically  by  the  reverse,  or  insulating  surface  of  each  wedge. 

When  multiplex  local  circuits  are  extended  to  branch  offices  over  single 
conductors  as  here  shown,  it  is  necessary  to  " split"  the  multiplex  local  bat- 
tery switch  so  that  the  local  battery  will  be  removed  from  the  receiving  relay 
circuit.  The  pole-changer  local  circuit  will  then  be  connected  as  when  the 


DUPLEX  REPEATER 


391 


local  battery  switch  is  thrown  to  the  right,  and  the  receiving  relay  will  be 
connected  as  when  the  battery  switch  levers  are  thrown  to  the  left  (see  Figs. 
295  and  298). 

With  this  arrangement  the  sender  on  the  duplexed  line  gets  his  own 
writing  in  the  receiving  relay.     It  is  necessary,  therefore,  that  all  keys  in 


Branch  Office 


FIG.  353. — Branch  office  control  of  a  duplex  over  a  single  conductor  where  half 

repeater  not  available. 

circuit  at  the  branch,  main  and  distant  offices  be  kept  closed  when  not  being 
used  in  the  act  of  transmitting. 

The  act  of  interrupting,  or  "breaking"  the  sender  is  accomplished  in 
the  same  manner  as  if  the  circuit  were  being  operated  as  a  single  Morse  wire, 
and  although  transmission  may  be  carried  on  in  one  direction  only  at  a  time, 
the  arrangement  makes  possible  the  employment  of  the  highly  efficient 
duplex  between  terminal  offices. 


THE  O'DONOHUE  "SHUNT"  REPEATER 

In  the  operation  of  the  ordinary  duplex  or  quadruplex  repeater,  the 
tongue  of  the  polar  relay  is  required  to  travel  from  its  open  to  its  closed  con- 
tact point,  before  the  battery  circuit  controlling  the  operation  of  the  pole- 
changer  of  the  companion  set  is  closed,  with  the  result  that  in  the  operation 


392 


AMERICAN  TELEGRAPH  PRACTICE 


of  circuits  in  which  the  current  strength  is  not  up  to  standard,  the  duration 
of  contact  between  the  tongue  and  closed  contact  of  the  relay  may  be  too 
brief  to  permit  of  firm  and  solid  signaling.  Fig.  354  shows  the  theoretical 
wiring  of  a  repeater  arrangement  devised  by  J.  P.  O'Donohue,  which  has 
for  its  object  the  prolongation  of  the  " marking"  contact  of  the  pole-changer 
lever. 

By  referring  to  the  diagram  it 
will  be  seen  that  while  the  tongue 
of  the  relay  is  in  contact  with  its 
back-stop,  a  short-circuit  path  to 
ground  is  presented  to  the  local 
battery,  which  shunts  the  current 
from  the  electromagnet  windings 
of  the  pole-changer,  resulting  in 
the  release  of  its  armature.  When 


oU 

D 

•  PR 


40 V 
ISO 


FIG.  354. — O'Donohue  shunt  repeater. 


a  marking  current  is  impressed  upon  the  line  at  the  distant  station  the  re- 
sulting movement  of  the  relay  tongue  into  the  closed  position  occupies  a 
portion  of  the  time  of  the  marking  contact,  which  lessens,  to  an  equal  extent, 
the  duration  of  the  marking  contact  of  the  companion  pole-changer  tongue. 
The  O'Donohue  repeater  introduces  a  time  element  which  favors  the  marking 
contact,  as,  it  is  apparent  from  the  diagram  that  at  the  instant  the  relay 
tongue  departs  from  its  back  contact,  the  shunt  path  is  removed,  permitting 
current  from  the  local  battery  to  energize  the  pole-changer  magnet  without 
waiting  until  the  relay  tongue  has  completed  connection  with  its  front,  or 
closed  contact. 

WORKING  AN  INTERMEDIATE  MORSE  LOOP  IN  A  DUPLEXED  CIRCUIT 

In  leased  wire,  and  press  service,  it  is  sometimes  advisable  to  avail  of  the 
advantages  of  duplex  apparatus  at  terminal  offices,  and  still  maintain  one  or 


FIG.  355. — Operating  an  intermediate  Morse  loop  in  a  duplexed  circuit. 

more  intermediate  offices  between  terminals  where  it  is  possible  to  employ 
only  simple  Morse  equipment. 

Figure  355  shows  the  conventional  scheme  of  the  polar  duplex  at  two 
terminal  stations  A   and  B.     If  the  duplex  battery  connections  at  both 


REPEATER  TABLE  ARRANGEMENT 


393 


stations  are  made  so  that  opposite  " poles"  are  to  line  when  both  pole- 
changer  keys  are  closed,  an  intermediate  office  using  a  single-line  relay,  may 
be  connected  into  the  main-line  circuit  at  a  point  any  distance  from  either 
terminal  as  depicted  in  the  sketch.  So  far  as  the  intermediate  office  is  conr- 
cerned  the  circuit  is  operated  in  the  same  manner  as  a  single  line  is  operated : 


V /  V /  '  I       y 


Id         lo  | 

LightninQ 
A?re*W?. 


pnQQQ 

looo 

|oj          L— P^ 


— tl 


Mil-Ammcier 


»   i 


FIG.  356. — Ariangement  of  apparatus  on  repeater  tables  in  Western  Union  service. 

opening  the  key  at  the  intermediate  office  opens  the  main-line  circuit,  which 
results  in  the  tongues  of  the  polar  relays  at  the  terminal  stations  being  moved 
into  the  spacing  position  due  to  current  traversing  their  compensation 
circuits  only,  and,  as  while  both  keys  are  closed  at  the  terminal  stations 
unlike  battery  poles  are  to  line;  closing  the  key  at  the  intermediate  office 


394 


AMERICAN  TELEGRAPH  PRACTICE 


results  in  a  flow  of  current  through  the  main-line  coils  of  the  polar  relays  at 
the  terminal  stations,  sufficient  in  strength  to  move  the  relay  tongues  into 
the  closed,  or  marking  position,  which  current  at  the  same  time  energizes 
the  magnet  of  the  intermediate  Morse  relay.  Thus  the  operation  of  the  key 
at  station  C  results  in  the  operation  of  the  polar  relays  at  both  terminal 
stations. 

When  station  A  is  sending  it  is  necessary  that  station  B  keep  the  key 
closed,  and  vice  versa.  It  is  evident,  for  instance,  that  while  the  key  at  B 
remains  closed,  closing  the  key  at  A  results  in  all  relays  being  energized,  and 


FIG.  357. — Multiplex  repeater  instrument  rack  used  in  "Postal"  offices. 

that  opening  the  key  at  A — thereby  presenting  like  poles  to  line  at  each  end 
of  the  circuit — results  in  cessation  of  current  in  the  main  line,  with  a  conse- 
quent movement  of  all  relay  tongues  into  the  open,  or  spacing,  position. 
Figure  356  shows  the  proper  arrangement  of  apparatus  on  multiplex 
repeater  tables,  in  the  service  of  the  Western  Union  Telegraph  Company, 
while  Fig.  357  shows  a  photograph  of  the  type  of  sectional  multiplex  re- 
peater shelving  used  by  the  Postal  Telegraph-Cable  Company  in  offices 
recently  equipped.  Each  vertical  tier  of  four  shelves  accommodates  the 
complete  equipment  of  two  quadruplex  Isets,  one  quadruplex  facing  the 
aisle  on  each  side  of  the  rack. 


CHAPTER  XIX 
THE  PHANTOPLEX 

Phantoplex  apparatus  used  in  association  with  ordinary  Morse  equip- 
ment, permits  an  additional  superimposed  transmission  of  Morse  signals 
over  a  wire  that  is  at  the  same  time  being  operated  as  a  single,  duplexed, 
or  quadruplexed  circuit,  without  interference  between  the  two  methods 
of  signaling. 

The  operation  of  the  system  will  be  understood  by  considering  the 
arrangement  of  circuits  as  depicted  in  Fig.  358  which  shows  the  terminal 


Alternating  Current 
^^^^^^__m____ni  Dynamo 

FIG.  358. — Theory  of  the  phantoplex. 

office  switchboard  and  instrument  wiring  of  a  6o-cycle  phantoplex  superim- 
posed upon  a  line  which  is  also  being  operated  as  a.  single  Morse  circuit. 
A  combination  system  as  here  illustrated  may  be  used  for  two  trans- 
missions in  either  direction  at  a  time,  or  for  one  transmission  in  each  direction 
at  a  time.  The  combination  has  an  advantage  over  polar  duplex  systems; 
in  that,  double  transmission  may  be  carried  on  in  one  direction,  whereas, 
with  the  latter,  double  transmission  implies  that  one  message  at  a  time  in 
each  direction,  only,  can  be  transmitted. 

395 


396  AMERICAN  TELEGRAPH  PRACTICE 

The  system  is  particularly  useful  where  the  bulk  of  the  traffic  handled 
between  two  offices  moves  in  one  direction. 

Referring  to  the  diagram:  it  will  be  seen  that  the  ordinary  Morse  circuit 
extends  from  one  brush  of  the  direct-current  dynamo  to  the  battery  disk 
of  the  main  switchboard,  thence  via  the  vertical  strap,  shank  of  the  spring- 
jack,  and  one  side  of  the  double  wedge  on  the  left,  to  the  key  and  relay  of  the 
Morse  set.  Returning  from  there  to  the  other  side  of  the  double  wedge 
which  is  in  metallic  contact  with  one  face  of  another  double  wedge  having 
connected  with  its  opposite  conducting  surfaces,  the  terminals  of  the  second- 
ary winding  of  a  transformer. 

It  is  evident  in  the  diagram,  that  an  uninterrupted  circuit  extends  from 
the  direct-current  dynamo,  via  the  Morse  relay,  and  secondary  of  the 
transformer,  to  line  and  ground  at  the  distant  station. 

When  the  system  was  first  introduced,  frequencies  as  high  as  175  cycles 
were  employed  to  operate  the  phantoplex  relays,  but  it  was  found  that  the 
inductive  disturbances  created  in  adjacent  conductors,  especially  in  parallel 
telephone  circuits,  due  to  the  rapid  alternations  in  the  telegraph  wire,  were 
so  detrimental  to  the  general  service,  that  it  was  decided  to  use  frequencies 
no  higher  than  125  cycles  per  second,  even  though  the  efficiency  of  the 
" phantom"  circuit,  was,  as  a  result  thereof  considerably  reduced. 

Tracing  the  phantoplex  wiring,  it  will  be  seen  that  one  end  of  the  primary 
coil  of  the  transformer  is  connected  to  one  brush  of  an  alternating-current 
generator.  The  other  end  of  the  primary  coil  is  connected  to  the  tongue  of  an 
ordinary  transmitter,  which  is  operated  in  the  usual  manner  by  a  Morse 
key  and  local  battery  (not  shown).  The  other  brush  of  the  alternating- 
current  generator  is  connected  to  the  back  contact  of  the  transmitter  by 
way  of  an  adjustable  rheostat.  A  branch  wire  is  connected  with  the  first- 
mentioned  terminal  of  the  primary  coil,  forming  a  static  circuit  via  the 
phantoplex  relay,  condensers,  closed  contact  point  of  the  transmitter,  and 
tongue  of  the  latter,  to  the  opposite  terminal  of  the  primary  coil  of  the 
transformer. 

The  phantoplex  relay  is  equipped  with  a  very  light,  and  delicately  poised 
armature  to  which  a  light  tongue  is  attached.  The  tongue  is  normally  held 
in  contact  with  its  back-stop  by  the  action  of  a  light  retractile  spring. 

With  the  tongues  of  the  transmitter,  relay,  bug-trap,  and  sounder  in 
the  positions  shown  in  Fig.  358,  it  is  evident  that  the  phantoplex  transmitting 
keys  at  the  home  station  and  at  the  distant  station  are  closed,  for,  when  the 
operator  at,  say  the  distant  station,  closes  his  key  he  causes  the  tongue  of 
his  transmitter  to  open  the  primary  circuit  of  the  transformer  at  that  station, 
thereby  interrupting  the  flow  of  alternating  current  in  the  line  wire,  and, 
as  the  main-line  circuit  includes  the  upper  winding  of  the  transformer  at  the 
home  station,  there  will  be  no  induced  e.m.f.  in  the  lower  winding  of  the 
transformer  at  the  latter  station,  as  a  consequence  of  which  the  tongue 


THE  PHANTOPLEX 


397 


of  the  home  phantoplex  relay  will  make  contact  with  its  open  point,  thereby 
closing  the  bug-trap  relay  circuit,  which  in  turn  closes  the  reading  sounder 
circuit.  When,  on  the  other  hand,  the  distant  office  opens  his  key,  the 
action  results  in  the  tongue  of  the  distant  transmitter  closing  the  alternating- 
current  generator  circuit  through  the  primary  coil  of  the  transformer  at  that 
station,  causing  a  high  frequency  alternating  current  to  be  induced  in  the 
upper  winding  of  the  transformer,  and,  as  the  upper  winding  is  included  in 
the  main-line  circuit,  the  alternating  current  is  transmitted  over  the  line, 
energizing  the  upper  winding  of  the  home  transformer  which  induces  a 
similar  current  in  the  lower  winding,  causing  the  phantoplex  relay  connected 
therewith  to  attract  its  armature,  thereby  opening  the  bug-trap  and  reading 
sounder  circuits. 

To  Wedge 


Transformer 
A.C.ben'r 


Sounder 


FIG.  359. — Phantoplex  without  bug-trap  relay. 


The  operation  of  the  phantoplex  is  easily  memorized  if  it  is  remembered 
that  the  high  frequency  current  is  impressed  upon  the  line  when  the  trans- 
mitter key  is  open,  not  when  the  key  is  closed,  and  that  the  reading  sounder 
is  closed  when  the  phantoplex  relay  is  "open." 

When  a  single  Morse  circuit  has  a  phantoplex  circuit  superimpcsed 
upon  it,  the  Morse  relays  do  not  respond  to  the  dots  and  dashes  formed 
by  the  alternating-current  impulses,  owing  to  the  fact  that  when  the  Morse 
keys  are  closed,  the  direct  current  from  the  Morse  battery  is  of  sufficient 
strength  to  hold  the  relay  tongues  in  the  closed  position  and  when  any 
Morse  key  in  the  circuit  is  open,  the  retractile  springs  attached  to  the  levers 
of  the  Morse  relays  are  strong  enough  to  hold  the  levers  against  their  back- 
stops. Careful  adjustment  of  the  Morse  relays  is  necessary,  but  if  the 


398 


AMERICAN  TELEGRAPH  PRACTICE 


direct-current  strength  is  not  less  than  75  milliamperes,  and  the  retractile 
springs  are  adjusted  to  have  a  strong  "pull,"  under  ordinary  circumstances 
the  Morse  relays  will  be  unaffected  by  the  high  frequency  currents  passing 
over  the  line. 

In  case  there  are  intermediate  Morse  stations  in  circuit  between  the 
terminal  stations  where  the  phantoplex  sets  are  installed,  it  is  necessary  to 
bridge  each  intermediate  office  with  a  condenser,  so  that  when  the  Morse 
key  at  any  office  is  opened,  the  phantoplex  currents  will  have  an  uninter- 
rupted path. 

Figure  359  shows  the  binding-post  connections  of  a  phantoplex  set  as 
installed  at  a  terminal  office  where  leg-board  facilities  are  available.  In 
the  arrangement  here  shown,  the  set  is  wired  so  that  the  phantoplex  relay 
local  contact  points  control  directly  the  operation  of  the  reading  sounder, 
without  the  intermediary  of  a  bug-trap  relay. 

THE  POLAR  PHANTO-QUADRUPLEX 

The  phantoplex  can  be  superimposed  upon  a  wire  that  is  already  being 
operated  by  the  differential  polar  duplex  or  quadruplex  systems  as  shown 


FIG.  360. — Phantoplex  duplex  superimposed  upon  a  polar  duplex  circuit. 

in  Fig.  360.  All  that  is  necessary  is  to  provide  a  static  path  for  the  alternat- 
ing currents  between  the  secondary  coil  of  the  transformer  and  the  earth 
at  the  stations  where  the  transformers  are  inserted  in  the  main-line  circuit, 
care  being  taken  to  connect  the  condenser  to  the  terminal  of  the  secondary 
winding  nearest  the  earth  contact,  and  on  the  opposite  side  of  the  trans- 
former to  which  the  main-line  wire  leading  to  the  distant  station  is  connected. 
For  the  best  results,  too,  it  is  necessary  that  the  artificial  lines  at  both  ends 


THE  PHANTOPLEX 


399 


Line 


FIG.  361. — Single  phantoplex  superimposed  upon  a  polar  duplex  circuit. 


N-«JUJUU/*L       Trcmstmr 
g  -  -  -  -  -  ^^stjiCTJBfrt ;  ] 

[  rronvmTj 


fl 

5Bridgealt  sets 
n 3 formgr |  back  of  thi 5- 


Transf'm'r      i« 


VAVWW 

Rheo. 


A.C.  A.C. 


FIG.  362. — Phantoplex  duplex  superimposed  upon  a  single  Morse  circuit. 


400 


AMERICAN  TELEGRAPH  PRACTICE 


of  the  circuit  be  so  built  up  that  they  will,  as  nearly  as  possible,  imitate 
the  resistance,  capacity,  and  inductance  of  the  real  line. 

The  phanto  quad  system  illustrated  in  Fig.  360  consists  of  a  phantoplex- 
duplex  and  an  ordinary  polar  duplex.  The  phantoplex  half  of  the  system 
takes  the  place  of  the  Stearns'  duplex  half  of  the  ordinary  differential  quad- 
ruplex.  The  sending  transformer  has  three  ceils  of  a  four-coil  transformer 
connected  in  series,  forming  the  secondary  winding.  The  outgoing  signals 
from  the  pole-changer  of  the  polar  side  pass  through  the  secondary  winding 
of  the  sending  transformer,  thence  differentially  through  the  polar  relay 
and  the  two  outside  windings  of  the  receiving  transformer,  without  affecting 
the  home  phantoplex  relay.  ^ 

An  incoming  signal  from  the  distant  pole-changer  passes  through  the 
primary  winding  of  the  receiving  transformer  without  inducing  a  current 
in  the  secondary  winding  of  sufficient  strength  to  operate  the  phantoplex 


Each  Coil  - 184-  Turns  #18  s.  c.  c.  c   Wire 
FIG.  363 .—Circuits  of  the  receiving  transformer. 

relay.  When,  however,  the  high  frequency  current  from  the  distant  alter- 
nating-current generator  passes  through  the  primary  of  the  home  receiving 
transformer,  a  current  is  induced  in  the  secondary  winding  of  the  required 
strength  to  operate  the  phantoplex  relay. 

Careful  consideration  of  the  action  taking  place  in  the  various  trans- 
formers when  phantoplex  currents  are  impressed  upon  the  line  at  each  end 
will  show  that  the  intended  signal  is  made  by  the  home  alternating-current 
generator  in  practically  the  same  manner  as  the  intended  signal,  in  the  case 
of  the  polar  duplex,  is  made  by  the  home  battery  through  the  compensation 
circuit,  when  like  poles  are  to  line  at  both  ends  of  the  circuit. 

Figure  361  shows  the  terminal  connections  of  a  single  phantoplex  circuit 
superimposed  upon  a  polar  duplex  circuit.  It  is  found  in  practice  that  the 
6-m.f.  condensers  shown  tapped  off  either  side  of  the  polar  relay  may  with 
equally  good  results  be  replaced  by  a  shunt  circuit  around  each  side  of  the 
polar  relay,  consisting,  in  each  case,  of  a  i6-c.p.,  22O-volt  carbon  incandescent 


THE  PHANTOPLEX 


401 


lamp,  furnishing  a  non-inductive  path  for  the  high  frequency  currents  out- 
side of  the  relay  coils. 

Figure  362  shows  the  instrument  and  transformer  connections  of  a  phanto- 
plex-duplex  superimposed  upon  a  single  Morse  line. 

THE  PHANTOPLEX  TRANSFORMER 

The  transformer  used  in  the  one  way  single  phantoplex  (Fig.  358)  has  a 
winding  ratio  of  i-i.     That  is,  the  primary  winding  and  the  secondary 


Primary  Coils  -386Turns#22s.c.c.c.Wirv. 
Secondary  Coil  »  2/0     »     #/9  „  „  ,, »   »  . 

FIG.  364. — Circuits  of  the  sending  transformer. 

winding  have  an  equal  number  of  turns  of  wire  of  the  same  size,  namely,  425 
turns  of  No.  19  B  &  S.,  gage,  single  silk-covered  wire  in  each  winding. 

Figure  363  shows  a  drawing  of  the  receiving  transformer,  indicating  the 
relative  positions  of  the  primary  and  secondary  coils.  The  resistance  of  the 
primary  winding  is  about  9  ohms. 

Figure  364  gives  a  similar  view  of  the  sending  transformer. 


2G 


CHAPTER  XX 

HIGH-SPEED  AUTOMATIC  TELEGRAPHY 
THE  WHEATS  TONE  AUTOMATIC 

Of  the  many  systems  of  automatic  telegraphy  invented  and  tried  out  in 
actual  service  since  the  Morse  telegraph  was  introduced  about  75  years  ago, 
the  system  which  has  been  most  extensively  employed  and  which  has  been 
found  to  answer  the  requirements  of  service  most  satisfactorily  is  that 
known  as  the  Wheatstone  Automatic. 

In  the  Wheatstone  system  of  automatic  telegiaphy,  the  dot  and  dash 
combinations  which  form  the  letters  of  the  alphabet  are  perforated  in  the 
Morse  code  on  specially  prepared  strips  of  paper  about  1/2  in.  in  width. 
When  the  letters  and  words  forming  the  message  or  messages  have  been 
perforated  in  the  paper  strip  the  latter  is  then  passed  through  a  Wheatstone 
transmitter  which  is  connected  into  the  main-line  circuit,  and  driven  by  an 
electric  motor. 

The  Wheatstone  transmitter  is  practically  a  high-speed  pole-changer 
operated  automatically  instead  of  by  means  of  a  Morse  key  in  the  hands  of  a 
telegrapher,  as  is  the  case  with  manually  operated  single  and  multiplex 
telegraphs. 

The  preparation  of  the  transmitting  tape  is  accomplished  by  means  of 
three-key  mallet  perforators,  or  by  keyboard  perforators,  which  may  be 
operated  by  any  telegrapher  after  a  little  practice. 

If  the  Wheatstone  transmitter  is  run  at  slow  speed  the  transmitted 
Morse  signals  can  be  read  by  sound  in  the  receiving  relay  (or  from  a  sounder 
connected  thereto)  in  the  same  way  as  hand  sending  may  be  read,  as  the 
Morse  is  plain  and  accurate.  When  the  motor  which  drives  the  transmitter 
is  speeded  up,  the  rate  at  which  signals  can  be  sent  over  the  line  may  reach 
300  or  400  words  per  minute,  depending  upon  the  speed  of  the  repeaters  in 
circuit — if  any  are  employed, — upon  the  KR  limitations  of  the  line  wire,  and 
upon  the  speed  at  which  the  polar  relay  at  the  receiving  end  of  the  line  will 
work  satisfactorily. 

It  is  the  usual  practice  to  operate  the  system  duplex,  which  means  that 
most  of  the  apparatus  of  the  ordinary  polar  duplex  is  retained.  At  the 
receiving  end  the  armature  of  the  polarized  relay  has  attached  to  it  an 
extension  arm  bearing  an  inking  wheel,  which,  when  the  tongue  of  the  relay 
is  in  the  spacing  position  (against  its  back-stop),  is  held  close  to,  but  not 
touching,  a  moving  band  of  paper  tape;  and  which,  when  the  tongue 

402 


HIGH-SPEED  AUTOMATIC  TELEGRAPHY  403 

of  the  relay  is  moved  into  the  marking  position,  makes  contact  with 
the  moving  paper  slip,  causing  an  ink  mark  to  be  made  thereon  of  a  length 
depending  upon  the  time  the  relay  tongue  is  held  in  the  marking  position. 
As  the  speed  at  which  the  tape  travels  under  the  inking  wheel  may  be  regu- 
lated to  suit  the  speed  of  the  received  signals,  each  word  received  by  the 
relay  will  appear  in  the  familiar  dot  and  dash  characters  marked  upon  the 
paper  strip. 

The  receiver  complete,  including  the  polarized  relay,  the  inking  gear, 
and  tape-moving  mechanism  is  known  as  the  Wheatstone  recorder. 

The  received  tape  is  passed  to  copyists  who  understand  the  Morse  code, 
and  who  translate  the  characters,  writing  the  message  on  a  received  telegram 
blank  by  means  of  a  pen  or  typewriter. 

Messages  received  by  the  automatic  system  at  any  office  for  relaying  to 
points  beyond,  may  be  translated  and  copied  as  above  described,  or  the 
received  tape  may  be  passed  directly  to  a  Morse  operator  who  transmits  the 
message  appearing  thereon  to  destination  by  hand.  If  the  message  is  to  be 
forwarded  from  the  relay  office  over  another  automatic  circuit,  the  received 
tape  must  be  translated  and  the  message  typewritten,  and  then  repunched 
on  transmitting  tape  as  at  the  originating  office,  so  that  it  may  be  passed 
through  the  automatic  transmitter  connected  into  the  second  circuit  and 
sent  over  the  line  at  high  speed. 

THE  MALLET  PERFORATOR 

The  perforator  which  is  shown  in  plan  and  front  elevation  at  a  and  b, 
Fig.  365,  is  purely  mechanical  in  its  action.  Groups  of  perforations  corre- 
sponding to  the  letters  of  the  alphabet  are  made  by  it  in  a  slip  of  oiled  paper 
which  is  afterward  propelled  automatically  through  the  transmitter. 

The  keys  or  plungers,  a,  a-i,  and  0-2,  actuate  five  steel  punches  used  in 
making  the  desired  perforations  in  the  moving  band  of  tape;  a,  corresponding 
with  a  "dot,"  0-1,  with  a  space,  and  a-2,  with  a  "dash. "  The  center  row  of 
perforations  acts  as  a  guide  to  keep  the  tape  in  its  proper  place  in  the  trans- 
mitter and  as  a  rack  by  which  it  can  be  propelled.  The  perforations  above 
and  below  the  center  determine  the  number  and  order  of  the  main-line  cur- 
rents sent  out  from  the  transmitter.  ' 

Figure  365^  shows  the  mechanism  of  the  perforator  placed  underneath 
the  metal  cover,  and  Fig.  365^  shows  the  levers  b,  b-i,  and  b-2,  which  are 
pivoted  in  the  block  B,  under  the  base,  and  connected  respectively  to 
the  keys  a,  a— i,  and  a— 2.  The  opposite  ends  of  the  levers  project  upward 
through  the  base  and  terminate  at  the  back  of  the  mechanism  near  the  ends 
of  the  five  steel  punches.  Above  and  below  the  punches  are  two  small  rods 
provided  with  steel  spiral  springs  for  withdrawing  the  punches  after  the 
depression. of  the  keys.  Spiral  springs  are  also  used  to  restore  the  keys  and 
levers  to  their  normal  positions  after  each  operation. 


404 


AMERICAN  TELEGRAPH  PRACTICE 


The  action  of  the  mechanism  in  perforating  the  paper  strip  is  rather 
difficult  to  learn  from  an  unavoidably  complicated  diagram,  and  it  may  suffice 
to  observe,  for  example,  that  in  perforating  the  word  "hat"  in  the  tape  the 
operator  depresses  the  key  a  four  times  in  forming  the  letter  "h"  then  the 


©00 


FIG.  365. — Mallet  perforator. 

key  a  once  and  the  key  a-2  once  in  forming  the  letter  "a"  and  then  the  key 
a-2  once  forming  the  letter  "t."  Between  each  two  letters  the  space  key 
0-i  is  depressed  once  and  between  words  twice,  in  order  that  the  letters  and 
words  of  the  message  will  be  properly  spaced  and  not  run  together  on  the 
receiving  tape  at  the  distant  station. 

ADJUSTMENT  OF  THE  PERFORATOR 

The  lever  h,  Fig.  365^,  is  connected  by  means  of  a  small  rod  passing 
through  the  base  to  the  lever  b-2,  and  is  only  actuated  when  a  dash  is 


HIGH-SPEED  AUTOMATIC  TELEGRAPHY 


405 


punched.  Its  function  is  to  regulate  the  movement  of  the  pawl,  e.  When 
either  a  dot  or  a  space  is  punched,  the  movement  of  lever  d-i  is  limited  by  the 
tail-piece  of  h,  and  the  pawl  moves  over  one  tooth  only  of  the  star-wheel,  push- 
ing the  tape  one  space  forward;  but  when  a-2  is  depressed  the  lever  h  is  raised 
so  that  the  movement  of  d-i  is  not  limited  by  h,  but  by  the  pin  /,  and  the  pawl 
accordingly  moves  over  two  teeth  of  the  star-wheel,  so  that  when  the  key 
rises  the  tape  advances  two  spaces. 

The  instrument  is  adjusted  by  means 
of  two  screws  i,  /,  which  act  upon  the 
bent  lever  k.  It  must  be  so  adjusted  that 
120  center  guide  holes  and  120  spaces  are 
produced  in  exactly  12  in.  of  paper  tape. 
The  adjustment  of  the  screws  i,  t,  moves 
the  lever  k,  either  inward  or  outward.  If 
the  end  nearest  the  punches  be  moved 
toward  them,  then  the  perforations  will 
be  spread  over  a  greater  length  of  tape; 
but  if  it  be  moved  away  from  the  punches, 
the  perforations  will  be  closer  together  and 
will  occupy  less  space.  If  a  length  of  slip 
be  taken,  containing  121  spacing  perfora- 
tions (which  number  may  be  obtained 
without  counting  by  punching  the  word  .  FlfG'  366.-Parts  of  the  mallet  per- 
J  •  f  orator,  i,  Front  puncher  plate;  2, 

message    four  times,  including  five  spaces  back  puncher  plate.  ^  back  guide  to 

between  words,  and  seven  spaces  at  the  punchers;  4,  back  spring  acting  on 
end  of  the  last  word),  then  the  distance  star  wheel  click  lever;  5,  vertical 
between  the  centers  of  the  first  and  last  spring  on  which  guide  roller  is  pivoted; 


holes  must  be  12  in. 


6' 


In  other  words,  the    ' 

wheel  click;  9, 
distance  between  the  centers  of  any  two 


7-  ****  "bed;  8  star 
star  wheel  click  lever; 
lever  regulating  play  of  star  wheel 
adjacent  guide  holes  must  be  exactly  one-  click  lever;  13,  center  punch  (for  dot, 
tenth  of  an  inch.  Although  a  perforation  dash  and  space);  14,  top  punch  (for 

more  or  less  will  not  make  any  material  dot  and  dash)'  J5,  bottom  Punch  <2' 
j'rc  ,1  T  .         .,    .    "     „  ,        j     i  for  dot  i  for  dash);  1  6,  center  punch 

difference  to  the  working,  it  is  well  to  ad-   ,,      ,    ,  . 

.  (for  dash);  17,  socket  lever;  18,  adjust- 

here  to  exact  spacing  when'  possible;  especi-  jng  jever 

ally  is  this   important  when  working  at 
high  speeds. 

The  flat  spring  g  can  be  adjusted  by  means  of  the  screws  n,  n-i  and  must 
exert  sufficient  force  to  propel  the  paper  freely  after  each  depression  of  the 
keys.  The  vertical  spring  which  carries  the  small  grooved  roller,  r,  is  ad- 
justable in  a  similar  manner  by  means  of  two  screws  under  the  base.  It 
should  exert  just  sufficient  force  to  cause  the  pawl,  e,  to  drop  between  the 
teeth  of  the  star-  wheel.  When  the  keys  a,  or  a-i,  are  depressed,  the  pawl 
should  move  freely  over  one  tooth,  and  when  the  key  a-2  is  depressed,  it 


406  AMERICAN  TELEGRAPH  PRACTICE 

should  be  drawn  back  over  two  teeth  of  the  star-wheel.  If  undue  force 
be  required  to  produce  this  action  between  the  pawl  and  the  star-wheel,  it 
will  probably  be  found  that  the  rubber  washer  under  the  head  of  the  faulty 
key  is  a  trifle  too  thick. 

The  star- wheel  frame  is  provided  with  a  tail-piece  which  projects  out- 
ward through  the  vertical  plate,  o,  on  the  left-hand  side.  When  paper  tape 
is  inserted  this  tail  is  pulled  toward  the  operator  in  order  to  move  the  star- 
wheel  out  of  the  way,  and  as  soon  as  the  tail  is  released,  the  star-wheel 
resumes  its  normal  position. 

Where  two  screws  are  provided  for  adjusting  the  lever,  care  should  be 
taken  always  to  release  one  before  tightening  the  other,  or  the  heads  are 
liable  to  be  broken  off,  the  thread  stripped,  or  the  standards  bent.  Lock- 
nut  screws,  or  clamping  screws,  also,  should  be  loosened  before  moving  the 
adjusting  screws  which  they  clamp,  and  carefully  tightened  again  after  the 
proper  adjustment  has  been  made. 

A  test  gage  1/2  in.  wide  and  0.009  m-  thick  should  pass  freely  between  the 
back  and  front  die-plates  of  the  perforator.  The  standard  width  of  perfora- 
tor tape  is  from  0.472  in.  to  0.475  m-  and  its  thickness  0.004  m-  to  0.0045  in. 

Figure  366  shows  the  various  parts  of  the  mallet  perforator,  each  part 
numbered  to  correspond  with  the  accompanying  list  of  parts. 

KEY-BOARD  PERFORATORS 

There  are  several  makes  of  key-board  tape  perforator  on  the  market, 
which  have  been  designed  to  take  the  place  of  the  mallet  perforator  in  the 
preparation  of  tape  for  transmission  by  means  of  automatic  transmitters. 
Among  these  might  be  mentioned  the  Gell  used  in  England  and  in  some  of 
the  British  colonies,  the  Kleinschmidt  perforator,  and  the  Storm  perforator 
made  in  the  United  States.  Fig.  367  is  a  reproduction  of  a  photograph  of 
one  of  these  perforators,  which  is  similar  in  appearance  to  all  other  makes. 

Figure  368  shows  a  key-board  arrangement  which  has  been  found  to 
answer  the  requirements  of  automatic  telegraph  service. 

The  Morse  characters  as  they  appear  in  perforations  in  the  tape  are  shown 
complete,  the  alphabet  used  being  American  Morse,  with  the  exception  of  the 
letter  "Z,,"  which  is  here  shown  as  consisting  of  one  dot,  a  space  and  three 
short  dashes,  instead  of  the  regulation  long  dash  of  the  Morse  code. 

THE  AUTOMATIC  TRANSMITTER 

Figure  369  shows  the  mechanical  construction  and  electrical  connections 
of  a  transmitter  arranged  to  operate  a  polar  relay,  the  latter  serving  as  a 
pole-changer  in  a  duplex  arranged  for  automatic  transmission. 

The  movements  to  and  fro  of  the  divided  lever  D-U,  are  regulated  and 


HIGH-SPEED  AUTOMATIC  TELEGRAPHY 


407 


FIG.  367. — Keyboard  tape-perforator. 


©©©©©©©©©© 

©  ®  ©  ®  ®  '©  @  O  ®  ® 

®-®  ©®©©®@®©© 
©@®©®®®®OQ® 


A        B       c      a    B     F       0        ft      i 


L  _  tr 


B      r      u        y       w       x         y       z        s l          B         a 


B  B  D  fXJUOff         COMMA        gUSST/OK  MAX. 


FIG.  368. — Keyboard    arrangement  of  tape  perforator,  showing  specimen  of  tape  after 

being  punched, 


408 


AMERICAN  TELEGRAPH  PRACTICE 


•i-IO 


o 
o 


r° 


I'- 


I 


,-c; 
> 

"2 


HIGH-SPEED  AUTOMATIC  TELEGRAPHY  409 

controlled  by  the  perforated  holes  in  the  paper  slip,  as  the  latter  is  moved 
along  from  right  to  left  by  the  star- wheel  W,  above  the  arms  5  and  M.  The 
transmitter  is  constructed  so  that  it  may  be  connected  directly  to  line,  the 
contact  points  Cu-Cd  and  Zu-Zd  acting  as  the  duplex  battery  terminals 
and  the  divided  lever  as  the  pole-changer  tongue  connected  to  the  main-line 
wire,  but  it  has  been  found  that  the  ranges  of  adjustment  are  not  so  limited 
where  the  automatic  transmitter  is  employed  to  operate  locally  a  polar 
relay,  the  tongue  of  which  is  connected  to  line  and  the  local  contact  points  of 
which  carry  the  main-line  potentials,  plus  and  minus.  The  upper  and  lower 
halves  of  the  divided  lever  D-U  are  mechanically  connected,  but  separated 
electrically,  that  is,  one  is  insulated  from  the  other,  so  that  either  the  lever 
D,  or  the  lever  U,  in  connection  with  the  lower  or  upper  contact  points 
respectively  Cd-Zd,  or  Cu-Zu,  may  be  used  to  operate  the  line  instrument. 
In  case  the  operation  is  transferred  from  the  upper  to  the  lower  contacts, 
or  vice  versa,  the  only  alteration  in  connections  required  is  that  the  ground 
contact  be  transferred  from  transmitter  binding-post  U  to  D  or  D  to  U,  as 
the  case  may  be. 

The  significance  of  the  letters  D  and  U  may  be  borne  in  mind  by  noting 
that  U  refers  to  the  upper  pair  of  contacts,  and  D  "down"  or  lower  pair. 

The  rocking  beam  is  equipped  with  two  pins  P,  Pf,  which  project  out- 
wardly. The  revolution  of  a  driving  wheel  (within  the  case  of  the  instru- 
ment and  not  shown)  which  is  fitted  with  a  projecting  pin  near  its  periphery, 
causes  the  rocking  beam  to  move  up  and  down  alternately  upon  a  central 
pivot.  The  pivoted  cranks  A  and  A '  are  held  against  the  under  side  of  pins  P 
and  P'  by  springs  attached  at  right  angles  to  the  lower  extremities  of  the 
cranks.  Rising  from  the  ends  of  the  two  cranks  are  the  rods  5  and  M. 
Actually,  the  rods-  are  side  by  side,  one  on  each  side  of  the  star- wheel  W. 
In  the  sketch  the  position  of  one  of  them  has  been  changed  somewhat  in 
order  to  show  both  rods.  Two  adjustable  screws  B  and  Bf  regulate  the  dis- 
tance backward  at  which  the  rods  may  be  set,  the  springs  Sf  and  S2  holding 
the  rods  against  the  screws.  In  their  upward  movement  the  rods  pass  through 
slots  cut  in  a  brass  platform.  As  the  perforated  tape  is  moved  along  the 
platform  by  the  star-wheel,  the  rods  continuously  moving  up  and  down 
enter  the  holes  in  either  side  of  the  tape  directly  as  these  holes  appear  over 
the  rods.  Above  the  star- wheel  is  mounted  another  wheel  a  trifle  wider  than 
the  tape  which  acts  to  hold  the  tape  down  and  permits  the  projections  of  the 
star-wheel  to  enter  the  center  row  of  holes  in  the  tape  and  thus  propel  it 
forward. 

With  the  transmitter  running  free,  that -is  without  tape,  rods  S  and  M, 
in  response  to  the  movements  of  the  rocking  aim,  rise  and  fall  alternately. 
The  lower  extremity  of  the  upright  section  of  crank  A  moves  to  the  right 
when  the  rod  S  moves  upward;  this  action  pushes  the  lever  acting  between 
the  contact  points  to  the  right  by  means  of  the  rod  and  boss  K.  The  up- 


410  AMERICAN  TELEGRAPH  PRACTICE 

ward  movement  of  the  rod  M  in  the  same  manner  causes  K  to  push  the 
lever  U  to  the  right.  Were  the  transmitter  connected  directly  to  line,  this 
action  would  mean  that  a  "make"  or  marking  current  would  go  to  line  at 
the  instant  the  rod  M  rises,  and  a  spacing  current  would  be  sent  to  line  when 
the  rod  S  rises.  Thus,  with  the  transmitter  running  without  tape,  a  series 
of  reversals  are  sent  out  producing  "dots"  in  the  distant  polar  relay. 

Inserting  a  strip  of  perforated  tape  in  the  transmitter  results  as  follows : 
Assuming  that  the  marking  rod  M  has  risen  and  entered  a  hole  in  the  tape 
and  that  the  tape  moves  forward  three  or  four  spaces  before  a  perforated  hole 
appears  above  the  rod  5,  then  the  marking  current  will  be  continued  until 
the  spacing  rod  S  has  an  opportunity  to  rise.  It  is  obvious  that  the  rod  6" 
has  in  the  meantime  continuously  bombarded  the  tape,  awaiting  the  first 
opportunity  to  travel  over  its  full  course  in  response  to  the  tension  of  the 
spring  53  and  which  it  has  been  prevented  from  doing  by  having  presented 
before  it  a  portion  of  the  tape  in  which  no  perforations  have  been  made. 
As  in  the  regulation  polar  relay,  the  lever  of  the  transmitter  must  remain 
on  either  closed  or  open-contact  point.  In  the  polar  relay  this  is  brought 
about  by  employing  permanent  magnets  to  hold  the  armature  in  either 
position.  In  the  transmitter  the  same  thing  is  accomplished  by  the  jockey 

wheel  /.  It  is  evident  that  as 
the  lever  moves  to  the  right  or 
left  it  is  held  in  either  position 

o  o        o  o  o  ^  by  the  action  of  the  spring  bear- 

ing down  the  jockey  wheel. 
Figure  370  shows  a  sketch 

FIG.  37o.-Specimen  of  perforated  tlpTbea'ing  the  of  the  Plated  slip  required 
word  "and."  to  transmit  the  word  "and." 

The  upper  holes  are  those  en- 
gaged by  the  rod  M  and  the  lower  ones  by  the  rod  S.  When  the  tape  is  in 
proper  position  in  the  transmitter  the  lower  holes  are  on  the  outward  side, 
or  toward  the  attendant,  the  tape  moving  from  right  to  left. 

When  unpunched  paper  is  inserted,  both  rods  S  and  M  are  pressed  down- 
ward and  the  pins  P,  Pf,  in  their  motion  do  not  actuate  the  crank  levers 
A,  A';  the  lever  DU,  consequently,  does  not  move  and  a  permanent  current 
is  therefore  sent  to  line. 

00 
If  now,  slip,  perforated,  say,  with  the  letter  °  °  °  (a)  be  inserted,  then, 

when  rod  M  rises,  it  will  be  free  to  pass  through  the  first  upper  hole,  and  the 
lever  DU  will  be  moved  and  will  send  out  a  "marking"  current.  When  the 
reverse  movement  of  the  rocking  beam  Y  takes  place,  rod  S  will  be  free  to 
pass  through  the  first  lower  hole,  and  the  current  sent  by  DU  will  be  reversed; 
a  dot  will  therefore  have  been  sent.  On  the  next  movement  of  the  rocking 
beam,  M  will  be  free  to  pass  through  the  second  upper  hole,  and  the  length 


HIGH-SPEED  AUTOMATIC  TELEGRAPHY  411 

of  the  " spacing"  current  is  consequently  precisely  equal  to  that  of  the  pre- 
vious " marking"  current  (dot).  The  " marking"  current  being  now  to  line, 
when  the  rocking  beam  leaves  S  free  to  rise,  it  is  prevented  from  so  doing 
by  the  paper,  which  is  not  perforated  below  the  second  upper  hole.  In  this 
case,  therefore,  the  " marking"  current  is  kept  on  until  the  rod  S  is  again 
free  to  rise,  which  it  can  do  through  the  second  lower  hole,  and  the  current 
is  then  reversed.  It  will  be  seen  that  the  "marking"  current  is  kept  to  line 
during  movements  equal  to  two  dots  and  the  space  between,  this  being  the 
established  length  of  a  dash.  It  is  clear,  therefore,  that  when  correctly  per- 
forated slip  is  run  through  the  transmitter  any  required  Morse  signals — 
dots,  dashes  and  spaces — can  be  automatically  sent  to  line. 

Adjustment:  One  end  of  the  flat  spring  which  carries  the  jockey  wheel 
/,  is  attached  to  a  brass  piece  F,  which  is  in  turn  screwed  rigidly  to  the  frame 
of  the  gearing.  The  upper  side  of  F  is  V-shaped,  and  the  tension  of  the  spring 
is  adjustable  by  means  of  the  two  screws  which  fasten  it  to  its  support.  It 
should  have  sufficient  tension  to  enable  it  to  push  the  lever  DU  suddenly 
to  the  right  or  left  when  either  of  the  collets  K  or  Kr  push  it  beyond  the 
center  of  the  jockey  wheel. 

The  collets  K  and  K'  can  be  adjusted  by  being  screwed  forward  or  back- 
ward; their  correct  position  may  be  found  by  running  the  transmitter  with 
a  blank  slip,  when  the  bar  should  remain  unaffected,  whether  resting  in  its 
right  or  left  position.  The  collets  must,  however,  be  sufficiently  close  to 
push  the  bar  over  the  center  when  the  slip  is  removed,  so  as  to  allow  the 
jockey  roller  to  complete  the  movement. 

In  order  to  insure  reliable  action  at  high  speed,  it  is  essential  that  the 
spiral  springs  5-3  and  5-4  be  strong  enough  to  easily  overcome  the  tension 
of  the  flat  spring  acting  through  the  jockey  wheel  upon  the  lever.  The 
amount  of  play  allowed  between  the  contact  screw  C-d  and  the  lever  D 
when  it  is  resting  on  Z-d,  or  vice  versa,  is  about  5  mils.  The  contacts  C-u 
and  Z—u  should  be  adjusted  to  suit,  so  as  to  preserve  similar  distances  with 
respect  to  U. 

The  exact  positions  of  the  vertical  rods  5  and  M  are  regulated  by  the 
screws  B,  B' ;  each  of  the  rods  should  be  so  adjusted  that  it  commences  to 
enter  a  perforation  in  the  slip  when  the  left-hand  edge  of  the  perforation  is 
sufficiently  clear  of  the  left-hand  edge  of  the  rod  to  allow  it  to  pass  through 
freely.  If  the  screws  P  or  P'  are  screwed  too  much  either  way  out  of  their 
correct  position,  the  rods  will  catch  against  the  edges  of  the  perforation,  and 
the  mechanism  will  not  act  properly. 

The  springs  S—i  and  S-2  pull  the  rods  S,  M,  back  against  the  screws 
P,  P',  when  they  have  become  sufficiently  withdrawn  to  be  just  clear  of  the 
slip.  Although  these  springs  are  very  light,  they  must  be  strong  enough  to 
cause  the  rods  to  return  to  their  normal  positions  promptly. 


412  AMERICAN  TELEGRAPH  PRACTICE 

THE  MOTIVE  POWER  OF  THE  WHEATSTONE  TRANSMITTER 

Until  recently,  high-speed  transmitters  have  been  operated  by  weight- 
driven  gears,  and  while  this  method  permitted  the  employment  of  the  high- 
speed system  at  small  offices  not  equipped  with  sources  of  electric  power 
when  upon  occasion  a  small  office  was  called  upon  to  handle  for  a  few  days 
a  large  volume  of  business,  in  large  offices  where  automatic  equipment  is 
permanently  located  it  is  desirable  to  have  transmitters  which  are  driven 
by  electric  motors,  first,  to  obviate  winding  up  the  weight,  and  second  to 
obtain  constant  speeds. 

Transmitters  are  equipped  with  small  direct-current  motors  which  are 
run  at  constant  speed,  approximately  the  maximum  speed  of  the  motor. 
No  motor-control  rheostat  is  used.  An  extension  of  the  motor  shaft  is  fitted 
with  a  metal  disk  which  acts  as  a  friction  plate.  On  the  face  of  this  friction 
plate  rests  the  edge  of  another  small  disk  made  up  of  compressed  rawhide 
held  rigidly  between  two  brass  plates  by  means  of  which  the  disk  is  securely 
attached  to  its  axle.  The  end  of  the  armature  shaft  remote  from  the  friction 
plate  is  fitted  with  two  tension-springs  which  act  to  hold  the  plate  in  contact 
with  the  rawhide  disk.  The  axle  of  the  disk  has  on  one  end  a  pinion  gear 
which  operates  the  driving  axle  of  the  transmitter  by  means  of  a  clutch. 
The  opposite  end  of  the  axle  bearing  the  rawhide  disk  is  hollowed  out  cone- 
shaped  in  order  to  engage  the  point  of  the  adjusting  screw  which  determines 
the  position  of  the  rawhide  disk  on  the  face  of  the  friction  plate.  The  method 
of  regulating  the  speed  of  the  transmitter  is  founded  on  the  principle  that 
the  speed  through  space  of  various  points  from  center  to  periphery  of  a  re- 
volving wheel,  is  greatest  at  the  periphery  and  least  at  the  center.  The 
speed-regulating  screw  as  it  moves  the  axle  of  the  friction  disk  along,  results 
in  the  friction  disk  being  pushed  nearer  to  the  periphery  of  the  friction  plate, 
thus  increasing  the  speed  of  rotation  of  the  transmitter  driving  axle. 

As  there  is  no  spring  used  to  withdraw  the  axle  of  the  rawhide  disk  when 
it  is  desired  to  reduce  the  speed  by  causing  the  disk  to  take  up  a  position  nearer 
the  center  of  the  friction  plate,  it  is  evident  that  another  property  of  the  re- 
volving wheel  is  availed  of  to  accomplish  the  desired  end. 

It  is  well  known  that  the  upper  half  of  a  revolving  disk  or  wheel  has  a 
motion  in  the  reverse  direction  to  that  of  the  lower  half  and  any  device  in 
frictional  contact  with  the  side  of  the  wheel,  unless  restrained,  takes  on  a 
motion  of  translation  of  that  portion  of  the  wheel  with  which  it  is  irt  contact, 
thus  when  the  adjusting  screw  which  holds  the  friction  disk  up  to  its  work,  is 
withdrawn  the  natural  tendency  is  for  the  friction  disk  to  move  inward 
toward  the  center  of  the  friction  plate  and  the  speed  is  gradually  reduced. 

The  clock-work  gearing  which  drives  the  moving  contacts  of  the  trans- 
mitter proper  is  connected  with  the  driving  axle  by  means  of  a  universal  clutch. 
The  transmitter  proper  is  detachable  from  the  base,  the  armature  and  battery- 
contact  wiring  being  made  to  buffer  contacts.  When  the  transmitter  gets  out 


HIGH-SPEED  AUTOMATIC  TELEGRAPHY 


413 


of  adjustment  and  there  is  a  spare  unit  available  it  requires  but  10  or  12 
seconds  to  remove  the  defective  instrument  and  substitute  one  known  to  be 
in  working  order.  As  the  transmitter  is  set  in  place  the  buffer  contacts  en- 
gage their  corresponding  projecting  terminal  points  and  the  driving  clutch 
engages  the  driving  axle  without  any  action  on  the  part  of  the  attendant 
except  that  he  place  the  transmitter  in  proper  position  on  its  brass  bed-plate 
and  tighten  the  thumbscrews. 

Where  i  zo-volt  current  is  available,  it  is  customary  to  use  it  for  the  opera- 
tion of  the  transmitter  motor.  The  regulation  of  the  speed  of  the  transmitter 
(and  consequently  of  the  speed  of  transmission)  is  accomplished  by  means  of 
the  friction  drive.  A  hard  rubber  knob  mounted  on  one  side  of  the  transmitter 


OD 


© 


Motor 
Terminals 


r 


— D     D— 


MKC 
O 


FIG.  371. — Main  line  and  battery  connections  of  the  automatic  transmitter. 

case,  accessible  to  the  attendant,  permits  of  regulating  the  speed  at  which 
signals  are  sent  over  the  line,  ranging  from  10  words  per  minute  to  300  words 
per  minute. 

As  there  is  no  rheostat  control  of  the  motor  circuit,  it  is  well  to  have  a 
resistance  of  about  100  ohms  in  each  side  of  the  no-volt  circuit  to  prevent 
heating  of  the  motor.  & 

Revolving  the  shaft  of  the  motor  causes  the  rocking  beam  of  the  transmit- 
ter to  move  up  and  down  at  a  speed  corresponding  to  the  speed  at  which  the 
star-wheel  forwards  the  paper  strip.  These  two  related  movements  are 
accomplished  by  means  of  suitable  clock-work  gearing. 

Figure  371  shows  an  enlarged  view  of  the  transmitter  main  connections, 
where  the  automatic  transmitter  is  employed  to  operate  a  pole-changer  in 
the  form  of  a  standard  polar  relay.  The  terminals  K,  MKC,  and  MKZ  are 
not  used  except  when  the  duplex  line  potentials  are  connected  directly  to  the 
transmitter.  The  terminals  marked  —  and  +  show  where  the  no-volt 
motor  leads  are  to  be  connected.  When  a  polar  relay  is  used  to  control  the 


414  AMERICAN  TELEGRAPH  PRACTICE 

line  battery,  the  main- line  and  artificial-line  binding  posts  of  the  relay  are 
connected -to  the  terminals  Z  and  C,  and  the  terminal  U  or  D  is  grounded. 
Either  the  upper  or  lower  contacts  may  be  used  by  changing  the  ground  con- 
nection from  U  to  D,  or  vice  versa. 

The  Wheatstone  system  has  for  many  years  been  used  on  certain  lines  of 
the  Western  Union  Telegraph  Company,  and  within  the  past  year  or  two  has 
been  introduced  on  the  lines  of  the  Canadian  Pacific  Railway  Telegraph 
system,  in  the  operation  of  a  Pacific  cable  circuit  between  Montreal,  Que., 
and  Bamfield,  B.  C.,  with  repeaters  at  Fort  William,  Ontario,  995  miles  from 
Montreal,  and  at  Calgary,  Alberta,  1,256  miles  distant  from  Fort  William, 
also  at  Vancouver,  B.C.,  646  miles  from  Calgary.  The  distance  from  Van- 
couver to  Bamfield  is  115  miles,  including  80  miles  of  submarine  cable.  At 
Montreal  dynamo  current  is  used;  at  Fort  William,  Calgary  and  Vancouver, 
storage  battery  is  used,  and  at  Bamfield,  gravity  battery. 

On  the  Pacific  cable  circuit,  overland  through  Canada,  the  question  of 
speed  is  of  secondary  importance,  and  high  speeds  of  transmission  are  not 
aimed  at.  The  principal  object  in  employing  the  Wheatstone  system  is  to 
insure  accuracy.  Also,  a  material  advantage  accrues  from  the  fact  that  at  a 
given  speed  in  worols  per  minute,  Wheatstone  signals  on  account  of  their 
evenness  and  regularity,  "  carry  "  much  better  over  long  circuits  than  do  hand 
signals  at  the  same  speed,  resulting  in  fewer  calls  for  repetition  of  doubtful 
words  or  letters. 

At  a  speed  of,  say,  40  words  per  minute,  using  Wheatstone  transmission, 
the  total  amount  of  business  handled  over  a  circuit  in  a  day  exceeds  consider- 
ably the  amount  of  business  that  would  be  handled  during  the  same  period 
by  means  of  the  Morse  key;  where  the  sending  operator  does  not  exceed  a 
speed  of,  say,  40  words  per  minute.  This  is  due  to  the  fact  that  in  Wheat- 
stone  working  there  is  generally  2  or  3  ft.  of  slack  tape  which  has  been  per- 
forated, between  the  perforating  machine  and  the  transmitter,  so  that  the 
frequent  stops  made,  from  one  cause  or  another,  by  the  perforator  operator — 
the  sender — do  not  interrupt  the  continuity  of  line  transmission,  which  goes 
on  continuously  as  long  as  tape  is  fed  to  the  transmitter. 

Wheatstone  working  may  be  applied  to  any  polar  duplex,  or  polar  side  of  a 
quadruplex,  by  providing  a  three-point  switch  at  each  sending  end  for  the 
purpose  of  switching  the  automatic  transmitter,  or  the  Morse  key  into  circuit 
as  desired,  and  by  providing  a  similar  switch  at  each  receiving  end  for  the 
purpose  of  switching  the  line  wire  into  the  automatic  recorder,  or  the  regular 
polar  relay  as  desired. 

Where  speeds  above  150  words  per  minute  are  to  be  maintained,  it  is 
necessary  to  use  at  the  terminal  offices  and  at  repeater  stations  the  most 
efficient  and  " fastest"  polar  relays  obtainable,  otherwise  the  equipment  and 
connections  of  the  Wheatstone  automatic  duplex  are  the  same  as  those  of  the 
high  efficiency  duplex  (see  Fig.  237). 


HIGH-SPEED  AUTOMATIC  TELEGRAPHY  415 

THE  POSTAL  AUTOMATIC 

The  Postal  Automatic  Telegraph  System  is  identical  with  the  Wheatstone 
in  so  far  as  concerns  the  preparation  of  the  transmitting  tape,  and  the  trans- 
mission of  the  signals;  but  the  reception  of  the  signals  is  accomplished  in  an 
entirely  different  manner,  being  received  by  an  electromagnetic  punch,  or 
"  reperforator  "  which,  instead  of  marking  the  dots  and  dashes  of  the  letters 
on  the  receiving  tape  with  ink,  as  in  the  Wheatstone  system,  perforates  the 
characters  in  a  continuously  moving  strip  of  paper  tape,  the  received  tape 
resembling  the  transmitting  tape,  inasmuch  as  the  Morse  characters  appear 
thereon  in  a  series  of  perforations.  The  improvement  in  this  method  as 
compared  with  Wheatstone  recorder  reception,  is  that  the  received  tape  may 
be  passed  through  a  local  "  reproducer,"  and  the  messages  copied  by  ear 
from  an  ordinary  sounder. 

The  reproducers  are  motor  driven  and  are  under  the  control  of  the  repro- 
ducing operator  so  that  the  speed  of  reproduction  may  be  regulated  to  accord 
with  the  ability  of  the  operator.  At  his  convenience  the  tape  may  be  stopped, 
pulled  back  and  run  through  again  for  the  purpose  of  confirming  doubtful 
words.  In  practice,  therefore,  the  reproducing  operator  copies  from  a 
"sender"  over  whom  he  has  absolute  control  in  the  matter  of  speed  and  of 
repetition.  Moreover,  with  this  system,  messages  received  at  relay  offices 
for  points  beyond,  which  are  equipped  with  automatic  apparatus,  may  be 
relayed  automatically,  simply  by  passing  the  received  tape  through  an 
automatic  transmitter  of  the  reproducer  type.  In  this  case  the  reproducer 
operates  the  duplex  pole-changer  in  the  same  way  as  it  operates  the  sounder 
for  local  reproduction. 

The  Reperforator. — The  operation  of  the  receiving  punch,  or  reperfora- 
tor, will  be  understood  by  tracing  the  receiving  circuits  shown  theoretically 
in  Fig.  372. 

It  will  be  observed  that  here  the  main-line  polar  relay  of  a  duplex  instead 
of  operating  locally  a  reading  sounder,  as  is  customary  in  ordinary  duplex 
working,  operates  an  extra  polar  relay,  the  armature  lever  of  which  is  grounded 
through  a  6-m.f.  adjustable  condenser.  Two  double-spool  electromag- 
nets, M,  M',  of  the  reperforator  have  circuits  leading  through  their  windings 
from  2oo-volt  dynamos  of  each  polarity,  thence,  extending  to  the  open  and 
closed  contact  points  respectively  of  an  auxiliary  polar  relay.  The  "  punch  " 
magnets  control  the  movements  of  two  armatures  which  on  their  free  ends 
are  equipped  with  steel  punches,  P,  P}  about  1/16  in.  in  diameter,  and  i  in. 
long,  which  when  the  magnets  are  energized  are  driven  through  holes  (h,  h, 
Fig-  373)  in  a  die  plate,  and  perforate  holes  in  a  strip  of  paper  which  is  being 
drawn  through  a  slot  past  the  holes  in  the  die  plate,  the  slot  being  just  large 
enough  to  permit  free  passage  of  the  tape. 

The  tape  is  moved  forward  continuously  by  means  of  a  tape-transmission 


416 


AMERICAN  TELEGRAPH  PEACTICE 


and  take-up  gear,  operated  by  an  electric  motor  the  speed  of  which  is  regu- 
lated by  a  small  hand  rheostat. 

It  is  customary  to  adjust  the  receiver  from  hand  sending  at  the  distant 
station,  before  the  automatic  transmitter  is  connected  to  line.  A  closed 
key,  sending  a  marking  current  from  the  distant  station,  results  in  the  tongue 
of  the  home  main-line  relay  moving  over  to  its  front  contact,  thereby  pre- 
senting a  ground  contact  to  the  85-volt  dynamo  circuit  by  way  of  the  front 
contact  of  the  main-line  relay,  and  the  magnet  EM  of  the  auxiliary  relay, 
which  causes  the  latter  to  attract  its  armature  to  the  left,  permitting  the 
6-m.f.  condenser  to  empty  itself  of  the  negative  charge  which  it  had  accu- 
mulated while  the  tongue  of  the  auxiliary  relay  was  in  contact  with  the  negative 
battery  terminal.  The  process  of  reversing  the  charge  held  by  the  condenser 


FA 


o  o  o 
o  o  o 


^^M 

0°         \ 


E          T         5  G 

FIG.  372. — Theory  of  the  reperforator. 

from  negative  to  positive,  after  the  relay  tongue  makes  contact  with  the  posi- 
tive battery  terminal,  causes  the  magnet  M  to  momentarily  attract  its 
armature  A,  and  as  the  armature  lever  is  pivoted  at  B,  the  steel  punch  P 
is  driven  through  the  moving  strip  of  paper,  perforating  a  hole  near  the  lower 
edge  of  the  tape.  As  the  distant  key  is  opened  and  a  spacing  current  sent  to 
line,  the  home  line-relay  " opens,"  thereby  transferring  the  ground  contact 
presented  to  the  85-volt  dynamo  circuit,  through  the  magnet  EM'  of  the 
auxiliary  relay,  causing  the  lever  of  that  relay  to  move  into  contact  with  the 
opposite  local  contact,  whereupon  the  charge  held  by  the  condenser  is  changed 
from  positive  to  negative,  causing  momentary  magnetization  of  the  punch 
magnet  M',  the  result  of  which  is  that  the  armature  lever  actuating  the  upper 
steel  punch,  drives  the  latter  through  the  tape,  perforating  a  hole  near  its 
upper  edge.  The  horizontal  distance  between  the  two  holes  depends  upon 


HIGH-SPEED  AUTOMATIC  TELEGRAPHY  417 

the  time  elapsing  between  the  instant  the  marking  current  is  sent  out  and  the 
time  the  spacing  current  is  sent  from  the  distant  station.  If  the  positive  and 
negative  battery  contacts  made  by  the  distant  pole-changer  are  made  close 
together,  as  in  forming  the  letter  "e,"  the  holes  in  the  received  tape  appear 
as  at  "e"  in  the  specimen  slip,  Fig.  372.  If  a  greater  period  of  time  separates 
the  positive  and  negative  battery  applications,  as  in  forming  the  letter  "t," 
the  holes  in  the  receiving  tape  appear  as  at  "t,"  in  the  specimen  slip. 

The  steel  punches  are  adjusted  to  travel  forward  just  far  enough  to  go 
through  the  paper  and  make  a  clean  round  hole,  and  backward  just  far 
enough  to  clear  the  face  of  the  die-plate. 

In  view  of  the  fact  that  the  tape  is  passing  continuously  through  the  slot 
in  front  of  the  steel  punches,  the  act  of  punching  the  holes  must  be  accom- 
plished by  extremely  rapid  movement  of  the  punches  so  that  there  will  be 
no  tendency  to  tear  the  tape.  The  speed  at  which  the  punches  move  forward 
and  backward  in  response  to  the  operation  of  the  auxiliary  relay  is  regulated 
by  having  the  capacity  of  the  condenser  accurately  adjusted,  and  by  adjusting 
the  tension  of  the  strong  retractile  springs  S,  attached  to  the  armature  levers 
of  the  reperforator,  so  that  when  the  steel  punches  are  traveling  the  required 
distance  to  and  fro,  the  action  will  be  rapid  and  snappy. 

It  is  evident  that  the  tape  being  perforated  is  stopped  each  time  either 
the  upper  or  lower  punch  is  in  the  act  of  perforating  a  hole,  and  as  each 
punch  is  operated  many  times  per  second,  it  is  necessary  so  to  adjust  the 
tape-moving  mechanism  that  these  momentary  stoppages  are  compensated 
for  by  "slip"  in  that  part  of  the  gear  which  pulls  the  tape  through  the  slot. 

The  instruments  have  been  designed  to  do  this  satisfactorily,  and  it 
has  been  found  that  attendants  can,  with  little  practice,  learn  the  correct 
adjustment.  The  present  method  of  taking  care  of  the  received  tape 
coming  from  the  reperforator  is  the  same  as  that  used  in  caring  for  the  original 
transmission  tape  as  turned  out  by  the  Wheatstone  perforator,  that  is,  by 
rolling  it  up  by  hand  as  it  comes  from  the  receiver. 

The  receiver  when  in  operation  requires  the  constant  attention  of  an  at- 
tendant, and  it  is  quite  convenient  for  him  to  take  care  of  the  received  tape 
in  the  manner  above  referred  to.  The  received  tape  may  be  parceled  out 
in  units  of  one  message,  two  messages,  or  in  any  number  required  by  traffic 
conditions,  as  the  receiver  attendant  very  quickly  learns  to  read  the  tape  and 
is  able  to  follow  the  wording  as  perforated  thereon.  The  end  of  each  message 

is  signified  by  a  paragraph  sign  ( )  or  by  a  succession  of  letters  "a," 

without  space  between  them. 

The  code  used  is  the  Morse  alphabet,  except  that  the  letter  "L"  is 

changed  from  "long  dash"  ( — ),  to  "dot,  three  dashes,"  ( ),  and  the 

figure  "nought"  from  "long  dash"  to  five  short  dashes  (--  — ). 

The  received  tape  is  passed  to  the  reproducing  operators  in  whatever 
size  bundles  the  traffic  demands,  and  by  them  is  run  through  local  repro- 

27 


418 


AMERICAN  TELEGRAPH  PRACTICE 


(D 


& 
m 


I 


« 


< 

fO 
t~^ 
fO 

d 

fe 


HIGH-SPEED  AUTOMATIC  TELEGRAPHY  419 

ducing  machines  at  a  speed  to  suit  the  convenience  of  the  operator  as  before 
stated. 

The  operation  of  the  reproducers  is  quite  simple,  and  may  be  learned  by 
any  Morse  operator  in  a  short  time  and  without  difficulty. 

Figure  373  shows  the  actual  construction  of  the  reperforator  used  in  con- 
nection with  the  Postal  automatic  telegraph  system,  the  various  parts 

bearing  the  same  index  letters  as  do  the 

Lock  Nut-., 
same  parts  illustrated  in  the  theoretical     Capstan 

diagram    Fig.  37*.    The  _  spring   adjust-  ^^ 
ments  bA,  are  for  regulating  the  retractile       . 
tension  exerted  by  the  springs  S,  upon  the 
armature   levers   A.     The   front    adjust- 
ment screws  FA  act  as  back-stops  for  the      FIG.  374.— Reperforator  bearing 
armature  levers,  and  must  be  so  set  that  adjustment, 

the  steel  punches  fastened  to  opposite  ends  of  the  levers,  when  pulled 
back  by  the  springs,  will  come  to  rest  in  the  punch  guide  holes  h,  just 
clear  of  the  face  of  the  die-plate.  The  lever  adjustment  screws  LA  ex- 
tend between  the  two  spools  of  each  magnet,  projecting  far  enough  to  prevent 
the  armature  striking  the  cores  of  the  magnet,  and  also  serve  as  adjustments 
for  regulating  the  distance  beyond  the  face  of  the  die-plate  the  punches  P 
are  allowed  to  travel.  The  forward  and  the  backward  travel  of  the  steel 
punches,  therefore,  is  regulated  by  means  of  the  adjusting  screws  FA  and  LA. 
In  practice,  a  forward  travel,  from  rest,  of  0.006  in.  is  all  that  can  be  allowed 
where  high  speeds  are  to  be  maintained. 

Figure  374  shows  an  enlarged  view  of  the  armature-shaft  bearing  of  the 
reperforator.  The  successful  operation  of  the  reperforator  is  largely  depend- 
ent upon  the  elimination  of  lost  motion  in  the  shaft  bearings,  and  the  bearing 
employed  while  somewhat  elaborate  is  the  only  one  among  those  tried  out 
which  satisfactorily  answers  the  purpose. 

The  parts  of  the  bearing  are  made  of  the  hardest  grade  of  Tobin  bronze, 
and  the  adjustment  is  made  as  follows: 

To  adjust  bearing:  Disconnect  retractile  spring  from  armature  lever. 
Tighten  screw  A,  leaving  just  space  enough  between  its  inner  surface  and 
the  surface  of  the  shaft  to  hold  a  film  of  oil.  Tighten  screw  B  of  each 
bearing  so  that  when  the  steel  punches  are  properly  lined  up  in  the  punch 
guide  holes  the  play  of  the  shaft  will  be  equal  in  the  bearing  A  on  each  side 
of  the  shaft.  Lock-nut  C  should  then  be  tightened,  securing  the  adjust- 
ment of  A,  care  being  taken  not  to  disturb  A  after  being  properly  set. 

The  reperforator  as  here  described  is  the  invention  of  Mr.  F.  E.  d'Humy. 

Figure  375  shows  the  transmitter  circuits,  arranged  so  that  either  the 
high-speed  automatic  transmitter,  or  a  Morse  key  operating  an  ordinary 
pole-changer  may  be  switched  into  circuit,  depending  upon  the  position  of  the 


420 


AMERICAN  TELEGRAPH  PRACTICE 


lever  of  the  switch  on  the  right.     The  duplex  " balancing"  switch  is  shown 
on  the  left. 

A  reading  sounder  circuit  for  the  out-going  signals  is  provided  by  means 


FIG.  375. — Transmitting  circuits,  Postal  automatic. 


FIG.  376. — Tape  take-up  gear,  Postal  automatic. 

of  a  2o,ooo-ohm  leak  to  earth  through  a  polar  relay  as  shown  in  the  lower 
left-hand  portion  of  the  diagram.  After  the  speed  of  transmission  is  run 
up  higher  than  65  or  75  words  per  minute,  the  sounder,  of  course,  fails  to 
record  the  signals  intelligibly. 


PRINTING  TELEGRAPHY 


421 


Figure  376  shows  the  construction  of  the  tape  take-up  gear. 

The  receiving  tape  is  fed  to  the  reperforator  by  a  tape  transmission 
device,  the  speed  of  which  may  be  regulated  to  suit  the  speed  of  signaling. 
As  the  perforated  tape  leaves  the  reperforator  it  passes  between  the  rollers 
T,  T',  of  the  take-up  gear,  which  are  in  light  contact  with  each  other,  the 
degree  of  tension  being  adjustable  by  means  of  the  compression-spring 
screws  E,  Ef.  A  spring  belt  extends  from  the  pulley  P'  to  a  pulley  mounted 
on  a  shaft  which  is  geared  to  the  driving  mechanism  of  the  tape-transmission 


FIG.  377. — Complete  wiring  connections  of  sending  and  receiving   circuits.     Postal 

automatic. 

gear  (not  shown),  and  the  speed  ratios  are  such  that  the  rollers  T,  Tf,  of  the 
take-up,  revolve  three  times  as  fast  as  the  feed  rollers  of  the  transmission 
device,  which  means  that  the  "pull"  of  the  rollers  T,  Tf,  is  not  positive  or 
constant.  It  is  necessary  that  there  shall  be  considerable  "slip"  of  the  tape 
as  it  passes  through  the  rollers  of  the  take-up,  for,  if  the  pull  were  positive 
the  tape  would  be  torn  during  the  brief  instant  that  either  of  the  steel  punches 
of  the  reperforator  are  punching  a  hole  in  the  tape.  The  combined  "slip" 
of  the  spring  belt  and  of  the  rollers  T,  T'  compensates  for  the  many  stoppages 
of  the  tape  which  take  place  during  the  operations  of  punching. 

Figure  377  shows  the  wiring  and  binding-post  connections  of  both  trans- 
mitting and  receiving  circuits  of  the  Postal  automatic  arranged  for  duplex 
operation. 

PRINTING  TELEGRAPHS 

Although  the  subject  of  printing  telegraphs  is  an  old  one  with  the  inventor 
and  with  the  promoter,  the  development  of  satisfactory  printing  telegraph 


422  AMERICAN  TELEGRAPH  PRACTICE 

systems  has  not  reached  that  stage  where  the  subject  is  in  shape  for  practical 
consideration  in  a  work  dealing  with  telegraph  practice. 

The  reason  for  this  (so  far  as  the  employment  of  printing  telegraph 
systems  in  America  is  concerned)  is  that  the  systems  which  have  been  tried 
out,  and  which  at  the  present  time  are  in  service,  have  been  operated  by  the 
inventors  themselves,  or  under  their  direction,  and  in  some  cases  by  specially 
trained  staffs,  recruited,  largely,  from  mechanics  who  know  little  or  nothing 
about  Morse  telegraphy. 

On  account  of  the  many  mechanical  movements  involved  in  the  operation 
of  telegraph  printers,  these  machines  are  necessarily  somewhat  complicated 
in  construction,  and  although  in  their  design  great  ingenuity  has  been 
exercised  in  applying  known  laws  and  principles  of  mechanics,  the  apparatus 
produced,  to  do  its  best  work,  must  be  handled  by  competent  mechanics. 
In  most  of  the  systems  so  far  introduced,  the  purely  electrical  features,  such 
as  line-potential  and  line-current  values,  and  main-line  relay  and  transmitter 
functions,  are  comparatively  simple,  and  it  is  with  these  features  only  that 
the  Morse  telegrapher  has  been  concerned. 

When  a  new  system  is  tried  out  in  service,  apparently  it  has  been  a  much 
easier  matter  to  teach  mechanics  what  they  need  know  about  the  electrical 
features  involved,  than  to  teach  the  expert  telegrapher  what  he  must  know 
about  mechanics,  in  order  to  operate  the  printer  efficiently.  These  considera- 
tions, in  a  sense,  isolate  the  subject  of  printing  telegraphs  from  the  subject  of 
Morse  telegraphy. 

It  is  not  to  be  inferred,  however,  that  printing  telegraph  systems  cannot 
be  employed  to  the  advantage  of  the  service,  as  it  is  cjuite  possible  that  the 
time  may  arrive  when  a  large  portion  of  the  telegraph  traffic  of  this  country 
will  be  handled  by  means  of  printing  telegraph  systems,  and  it  is  possible 
that  within  a  few  years,  one,  two,  or  more  systems  will  have  reached  a  stage 
of  development  and  of  standardization,  that  will  make  possible  a  technical 
treatment  of  the  subject  from  a  telegraphic  standpoint  that  will  be  intelligible 
to  Morse  operatives. 


NAMES  OF  PRINTING  TELEGRAPH  SYSTEMS  INVENTED,  TRIED  OUT,  AND 

IN  SERVICE 

Two  different  systems,  known  as  the  Rowland  and  the  Wright,  have 
within  the  past  few  years  been  tried  out  experimentally  on  the  lines  of  the 
Postal  Telegraph- Cable  Company.  Each  of  these  systems  was  the  product 
of  printing  telegraph  inventors  of  great  skill,  and  who  were  quite  familiar 
with  the  requirements  of  such  inventions. 

The  performance  of  the  Rowland  system  and  of  the  Wright  system 
was  excellent  under  certain  conditions  of  traffic,  but  both  have  been  taken 
out  of  actual  service  and  returned  to  the  laboratory  for  further  development. 


PRINTING  TELEGRAPHY  423 

The  Western  Union  Telegraph  Company  has  for  a  number  of  years 
past  been  using  a  printing  telegraph  system  known  as  the  Barclay  printer. 
Formerly  the  system  was  known  as  the  Buckingham,  in  which  certain 
changes  and  improvements  have  been  made  by  Mr.  Barclay. 

The  Buckingham-Barclay  printer  is  at  the  present  time  employed  com- 
mercially by  the  Western  Union  Company,  but  is  still  being  studied  with 
the  object  of  introducing  further  improvements,  or  of  making  alterations, 
in  order  that  the  machine  may  more  satisfactorily  meet  the  requirements  of 
modern  telegraph  traffic  conditions. 

In  British  Post-office  telegraph  service,  the  following  named  systems 
are  being  used  to  a  greater  or  less  extent:  The  Creed,  Murray,  Baudot,  and 
the  Hughes. 

In  the  United  States  at  the  present  time  a  printing  telegraph  system 
known  as  the  Morkrum,  is  being  tried  out  on  certain  lines 'of  the  Postal 
Telegraph- Cable  Company,  and  of  the  Western  Union  Telegraph  Company. 

In  Canada  the  Morkrum  system  is  being  tried  out  on  a  Canadian  Pacific 
Railway-telegraph  circuit  between  Montreal  and  Toronto. 

For  the  information  of  those  who  may  wish  to  study  the  historical  develop- 
ment of  printing  telegraph  systems,  or  who  may  desire  to  investigate  the 
principles  of  operation,  and  the  construction  of  printing  telegraph  machines, 
a  condensed  bibliography  of  printing  telegraph  literature  is  incorporated 
in  the  appendix,  see  section  A. 


CHAPTER  XXI 

TELEGRAPH  AND   TELEPHONE   CIRCUITS   AS  AFFECTED    BY 
NEIGHBORING  ALTERNATING-CURRENT  LINES 

TRANSPOSITION  OF  LINES  USED  FOR  TELEPHONE  PURPOSES    AND  FOR 
SIMULTANEOUS  TELEGRAPH    AND  TELEPHONE  PURPOSES 

It  is  well  known  that  when  current  flows  in  any  wire,  there  exists  in  the 
space  surrounding  the  conductor  an  electromagnetic  field,  extending  outward 
from  the  wire  to  an  indefinite  distance  and  gradually  diminishing  in  strength. 
If  the  current  traversing  the  conductor  is  alternating  in  polarity,  the  strength 
of  the  electromagnetic  field  is  continually  changing,  and  it  is  due  to  this 
change  in  strength  that  electromotive  forces  are  induced  in  neighboring 
conductors. 

Due  to  the  sign  of  the  e.m.f.  and  its  value  in  the  first-mentioned  conductor, 
there  is  an  electrostatic  field  extending  from  it  to  an  indefinite  distance  which 
decreases  in  strength  with  increased  distance.  The  electrostatic  field  induces 
charges  in  adjacent  conductors;  the  induced  charge  continually  changing  in 
sign — from  positive  to  negative  and  vice  versa — so  that  in  effect  there  is  in- 
duced in  the  neighboring  wire  an  alternating  current  as  a  result  of  both  elec- 
tromagnetic and  electrostatic  induction. 

It  is  true,  of  course,  that  electrostatic  and  electromagnetic  fields  exist  in 
the  space  surrounding  conductors  carrying  direct,  or  uni-directional  currents; 
but  in  this  case  it  is  only  the  rise  and  fall  of  the  current  strength,  with  the 
accompanying  rise  and  fall  of  the  field  strength  (generally  as  a  result  of  open- 
ing and  closing  the  circuit)  which  induces  disturbing  currents  in  neighboring 
conductors. 

The  disturbance  created,  so  far  as  the  effects  of  electrostatic  and  electro- 
magnetic induction  are  concerned,  in  the  case  of  the  former  depends  upon 
the  distribution  of  the  currents  of  charge,  which  is  proportional  to  the  rate 
at  which  the  electrostatic  field  changes.  In  the  case  of  the  latter  the  neigh- 
boring wire  has  induced  in  it  an  electromotive  force  proportional  to  the  rate 
at  which  the  strength  of  the  electromagnetic  field  changes. 

In  the  operation  of  telegraph  circuits  the  induced  disturbances  resulting 
from  the  proximity  of  the  conductor  to  other  conductors  carrying  direct 
currents,  generally  are  due  to  cross-fire  between  neighboring  conductors  of 
the  telegraph  system  on  the  same  pole  lines  (see  Cross-Fire,  page  209). 
Those  disturbances  due  to  atmospheric  electrical  phenomena  also  have  been 
referred  to  in  a  previous  chapter,  see  page  120. 

424 


INDUCTIVE  DISTURBANCES  425 

The  most  harmful  induction  experienced  in  the  operation  of  telegraph 
lines  is  that  due  to  neighboring  high-tension  power  lines  carrying  alternating 
currents. 

Numerous  plans  for  obviating  the  effects  of  induction  from  high-voltage 
alternating-current  power  lines  have  been  suggested,  some  of  which  have 
been  tried  out  in  practice,  the  results  in  most  cases  being  far  from  satisfactory. 

There  are,  however,  a  few  methods  of  getting  around  the  difficulty,  which 
have  considerable  merit,  and  which  when  properly  applied  make  possible 
the  operation  of  circuits  subject  to  inductive  disturbances,  which,  otherwise 
would  be  inoperative  as  long  as  the  physical  relations  of  the  two  lines  remained 
unaltered. 

One  of  these  methods  requires  that  two  wires  be  used  for  each  telegraph 
circuit,  thus  forming  a  metallic  circuit  in  place  of  the  usual  single  grounded 
conductor  (see  Fig.  266,  "The  Metallic  Circuit  Quadruplex")- 

Among  the  other  methods  proposed,  might  be  mentioned  those  covered 
by  U.  S.  patents,  Nos.  955,141  and  955,142,  issued  to  Mr.  Minor  M.  Davis. 
The  first  covers  the  placing  of  an  idle  conductor  in  close  proximity  to  a  tele- 
graph conductor  so  that  both  of  these  conductors  are  subject  to  the  induction 
from  the  disturbing  source,  and  affected  to  the  same  extent.  The  currents 
induced  in  the  idle  conductor  will  react  upon  the  telegraph  conductor  and 
this  reaction  may  be  adjusted  so  as  to  compensate  or  neutralize^ the  action 
of  the  disturbing  circuit  upon  the  telegraph  conductor.  Or,  stated  specif- 
ically, a  positive  impulse  in  the  disturbing  wire  induces  a  negative  impulse 
in  the  telegraph  wire  and  also  in  the  idle  conductor,  the  negative  impulse 
in  the  idle  conductor  reacts  tending  to  produce  a  positive  impulse  in  the 
telegraph  circuit.  By  regulating  the  resistance  and  capacity  of  the  idle 
conductor,  the  impulses  resulting  from  the  reaction  of  the  idle  conductor 
may  be  made  to  counteract  the  disturbing  impulses  in  the  telegraph  circuit. 

This  plan  of  induction  neutralization  is  especially  applicable  to  telegraph 
conductors  in  aerial  cables  suspended  on  pole  lines  parallel  to  high-tension 
lines.  To  attain  the  desired  ends  the  telegraph  wires  extending  through 
the  zone  of  disturbance  may  be  cabled.  The  conductors  in  the  cable  consist- 
ing of  two  groups  arranged  parallel  and  insulated  from  each  other.  The 
wires  of  one  of  these  groups  being  used  for  signaling  purposes  while  the 
other  group  of  wires — the  idle  conductors — are  tied  together  at  each  end  of 
the  cable.  At  one  end  of  the  cable  the  joined  idle  conductors  are  connected 
to  ground  through  an  adjustable  resistance,  and  at  the  other  end  of  the  cable 
to  ground  through  an  adjustable  capacity. 

With  this  arrangement  a  positive  impulse  in  the  disturbing  wire  induces 
an  impulse  of  the  opposite  sign  in  all  of  the  conductors  in  the  cable.  If  the 
resistance  and  the  capacity  of  the  idle  conductors  is  properly  adjusted  this 
negative  impulse  will  be  so  proportioned  in  its  effect  upon  the  telegraph 
conductors  that  the  induced  impulse  from  the  disturbing  wire  will  be  neu- 


426  AMERICAN  TELEGRAPH  PRACTICE 

tralized.  Obviously,  the  idle  conductor  does  not  need  to  be  as  long  as  the 
telegraph  wire,  but  by  establishing  the  constants  of  the  idle  conductors — 
capacity  and  resistance — at  the  most  effective  values,  an  effect  is  produced 
which  tends  to  compensate  for  the  effect  of  the  disturbing  wire  upon  the 
telegraph  conductor. 

The  other  plan  aims  to  neutralize  induction  in  parallel  circuits  by  employ- 
ing as  a  conductor  the  metal  sheath  of  the  cable  inclosing  the  telegraph  con- 
ductors and  a  parallel  compensating  conductor,  all  of  which  are  subject  to 
the  same  inductive  influence,  and  causing  the  induced  impulses  in  the  com- 
pensating conductor  to  react  upon  the  telegraph  conductor  to  an  equal  and 
opposite  extent  as  compared 'with  the  disturbing  cause. 

Where  there  are  one  or  more  insulated  conductors  in  parallel  relation,  con- 
nected in  circuit  with  telegraph  apparatus  in  the  ordinary  manner,  parallel  or 
with  these  conductors,  as  in  the  same  cable,  are  one  or  more  compensating 
conductors;  these  are  connected  in  a  circuit  susceptible  of  conveying  induced 
impulses,  and  for  this  purpose  there  may  be  used  a  ground  return  circuit,  or 
the  circuit  may  include  a  condenser.  One  coil  of  a  transformer  is  connected 
in  this  circuit  and  the  other  coil  of  the  transf  orner  is  connected  in  circuit  with 
a  conductor  arranged  parallel  with  the  disturbing  source,  for  this  purpose 
there  may  be  used  a  separate  conductor  or  the  metal  sheath  or  armor  of  the 
cable  included  in  a  compensating  circuit  may  be  used,  and  the  transformer  so 
adjusted  that  the  compensating  conductors  will  develop  a  source  of  alternating 
current  having  an  electromotive  force  efficient  to  compensate  for  the  induc- 
tive effect  of  the  disturbing  source.  If  the  disturbing  source  extends  parallel 
to  the  telegraph  conductors  for  a  comparatively  long  distance  there  may  be 
one  or  more  compensating  conductors  arranged  parallel  with  the  telegraph 
conductors  for  a  much  shorter  distance,  but  the  electromotive  force,  intensity 
or  current  strength  is  increased,  graduated  or  adjusted  so  as  to  compensate 
and  neutralize  the  effect  of  the  disturbing  cause  in  the  telegraph  conductors. 

An  effective  and  inexpensive  method  of  screening  the  Morse  relays  in  a 
grounded  telegraph  circuit  from  the  effects  of  induction  from  a  neighboring 
high-tension  line  is  illustrated  schematically  in  Fig.  378. 

At  each  end  of  the  section  of  telegraph  line  exposed  to  the  high-tension  line 
a  low-resistance  choke  coil  is  included  in  the  telegraph  circuit,  and  on  the  line 
side  of  each  choke  coil  a  condenser  path  to  ground  is  presented  to  the  induced 
currents.  This  arrangement  is  quite  effective  where  the  disturbance  is  not 
great,  and  where  ground  potentials  have  a  low  value  and  have  a  constant 
polarity. 

Figure  379  shows  a  method  of  screening  the  Morse  relay  at  a  way  office 
on  a  single  circuit,  wherein  an  alternative  path  is  presented  to  the  induced 
alternating  currents,  enabling  them  to  pass  through  the  station  with  mini- 
mum effect  upon  the  relay. 

Figure  380  shows  an  excellent  terminal  or  way-office  arrangement  for  use 


INDUCTIVE  DISTURBANCES 


427 


Power  Line 


Relay 

IOOM                                         100" 

Relay 

T     w 

=• 

IR 

*= 

=  Imf                          = 

-                                    •= 

IR 
•=lmf. 

F 

W       T 

•= 

FIG.  378. — Telegraph  circuit  in  close  proximity  to  high-tension  power  line. 


Line 


100  w 
IR 


. 


100"       .  »,.     , 
T  R         ItolSmfi 

FIG.  379. — Method  of  screening  way  office  relay  on  a  single  line. 


5  K.  30  Ohm 
Inductance  Coil 


10  00  Ohms 


>6tvl8M.F. 


5K.  50  Ohm  Adjustable    Nots:  5K,  Coils  inductively 

Inductance  Coil          (,vnaenser  connected  in  series. 

Single  Set 

FIG.  380.— Terminal  office  or  way  office  relay  on  a  single  line  protected  against  induction 
from  neighboring  high-tension  lines. 


P.O. 


2  Col  Is 

16000  Turns  No.30/ 

7?5  Ohms  Each, 

Differential 


1M.F. 


TT 

Air  Core' 

^Impedance  Co!  1 

e*L 

^5000  Turns  No.24 

JU  Adjustable  Non  - 
1L   Inductive  Resistance. 

T  ^=^   Polar 

r^°Re/ay 

\  Resistance  of  Shunt 
should  be  kept  low. 

k     1 

0 

^Adjustable 

Duplex  Set 

'AL. 

FIG.  381. — Duplexed   line   protected    against    disturbances    from    neighboring    25-cycle 

high-tension  line. 


428  AMERICAN  TELEGRAPH  PRACTICE 

on  single  lines,  employing  standard  5^  coils  for  the  purpose.  In  this  arrange- 
ment the  relay  winding  is  shunted  with  a  i,ooo-ohm  non-inductive  resistance 
forming  one  branch  of  a  resonant  circuit  which  provides  a  path  past  the  relay 
for  the  induced  alternating  currents. 

Figure  381  shows  the  theoretical  main-line  connections  of  a  differential 
polar  duplex  equipped  with  protective  coils  and  condensers  for  off-setting  the 
effects  of  induction  from  25-cycle  single-phase  power  circuits. 

In  balancing  duplex  or  quadruplex  sets  connected  into  lines  that  are  affected 
by  heavy  induction,  the  constant  chattering  of  the  relays  when  the  main-line 
battery  at  both  ends  of  the  line  is  removed  by  throwing  the  ground  switches 
to  the  left,  makes  it  quite  difficult  to  determine  when  the  polar  relay  has  been 
balanced  magnetically. 

In  cases  where  it  is  important  that  the  magnetic  balance  should  be  accu- 
rate it  is  necessary  to  place  the  lever  of  the  ground  switch  in  the  center,  and 
to  open  the  artificial  line  and  condenser  circuits  by  throwing  the  rheostat 
switch  and  retardation  resistance  coil  switch  into  the  "open"  position. 

TRANSPOSITION  OF  WIRES  ON  POLE  LINES 

When  two  single  wires  of  a  telegraph  system  are  joined  together  at  terminal 
stations  for  the  purpose  of  providing  a  metallic  telephone  circuit,  it  is  neces- 
sary that  the  wires  should  be  transposed  at  predetermined  intervals  along  the 
line  in  order  that  there  will  be  no  "cross-talk"  effects  between  the  telephone 
circuit  thus  formed,  and  other  telephone  circuits  on  the  same  or  adjacent  pole 
lines.  Transposing  the  two  sides  of  the  telephone  circuit  as  above  indicated 
also  protects  the  telephone  circuit  from  the  effects  of  induction  from  neighbor- 
ing power  lines,  trolley  line,  and  telegraph  circuits. 

Through  those  sections  of  the  line  where  the  conductors  are  carried  in 
aerial  or  underground  cables,  transposition  is  effected  by  twisting  the  two 
conductors  of  each  metallic  circuit  around  each  other  continuously,  forming 
what  are  called  "twisted  pairs." 

There  are  several  theoretical  methods  of  determining  the  number  of  trans- 
positions necessary  in  a  given  distance,  to  protect  the  circuit  from  mutual  and 
from  foreign  induction,  where  reasonably  definite  values  can  be  determined 
for  the  various  factors  involved,  but  in  practice  it  is  found  advisable  not 
to  adhere  too  closely  to  the  dictates  of  theory  in  this  regard,  but  rather  to 
provide  sufficient  margin  to  offset  any  possible  additions  to  the  sources  of 
disturbance. 

Standard  practice  in  locating  the  position  of  transposition  poles  is  to 
measure  a  distance  of  1,300  ft.  from  the  first  pole  of  the  line  and  mark  the  pole 
nearest  to  the  point  so  measured  A.  Then  measure  successive  distances  of 
1,300  ft.  each,  and  letter  the  nearest  poles  B,  C,  B,  A,  B,  C,B,  A,  B,  C,  etc., 
successively,  the  circuits  being  transposed  upon  the  poles  so  lettered  as 


TRANSPOSITION  OF  CONDUCTORS  429 


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FlG    382.— Transposition  of  wires.     Four-pin  cross-arms. 


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JTIG    383.— Transposition  of  wires.     Six-pin  cross-arms. 


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T  FIG.  384.— Transposition  of  wires.     Eight-pin  cross-arms. 


- -,-~-?i300 '  Upper  Crossarm 


Lower  Cro6sarm 
FIG.  385. — Transposition  of  wires.    Ten-pin  cross-arms. 


430 


AMERICAN  TELEGRAPH  PRACTICE 


shown  in  Fig.  382.  The  diagram  shows  the  necessary  transpositions,  where 
two  circuits  are  carried  on  the  upper  cross-arm  and  two  on  the  lower  arm. 

Figures  383,  384  and  385  show  respectively  the  scheme  of  transposition 
for  six-pin,  eight-pin  and  ten-pin  arms. 

All  transpositions  in  copper  circuits  are  made  by  cutting  the  wires  on 
the  pole  side  about  20  in.  from  the  cross-arm,  and  slipping  on  each  half  a 


B    —pgygrea—  fr    g^ST^gegP  A 

FIG.  386. — Method  of  transposing  wires  at  supports. 

Mclntyre  sleeve,  with  which  the  wires  on  the  cross-arm  side  are  dead-ended, 
one  in  the  lower  groove  and  one  in  the  upper  groove  of  the  transposition 
glass  insulator,  allowing  the  ends  to  project.  About  6  ft.  of  slack  wire  is 
then  joined  to  the  wires  on  the  cross-arm  side  by  using  a  whole  Mclntyre 
sleeve.  Half  sleeves  are  then  slipped  on  and  the  wires  dead-ended  in  the 


upper  grooves.    ransposing 
'insulator/.'  Wire    betrree 
insulator  "c'* 


Wires  fa"  and  "d"  fastened 

*e"and   h".    Wires  '&"  and'c 

wire    "between  wires *# "A  "C 

"ct'and  "d" 


FIG.  387. — Transposition  of  wires,  carried  on  end-pins. 

vacant  grooves  of  the  insulators,  after  which  the  free  ends  are  crossed  and 
connected  by  half  sleeves  as  shown  in  Fig.  386. 

Where  the  wires  to  be  transposed  are  located  on  either  end  of  the  cross- 
arm,  transposition  is  effected  by  supporting  the  two  cross  wires  upon  bracket 
pins  as  shown  in  Fig.  387. 


TRANSPOSITION  OF  CONDUCTORS 


431 


The  transposition  insulator  consists  of  two  single  insulators  on  the  same 
pin  as  shown  in  Fig.  388.  The  lower  section  has  no  top,  and  the  pin  projects 
through  it,  the  upper  insulator  being  secured  on  the  top  of  the  pin  in  the  usual 
manner. 

Figure  388  on  the  left  shows  a  standard  insulator,  and  on  the  right  a 
transposition  insulator. 


Standard  insulator 


Transposition  insulator. 


FIG.  388. 


Instead  of  transposing  wires  on  the  glass  insulators  screwed  on  wooden 
pins  inserted  into  the  tops  of  cross-arms  in  the  usual  manner,  it  is  now  com- 
mon practice  to  employ  iron  /  hooks  driven  into  the  cross-arm  from  the  un- 
der side.  A  regulation  glass  insulator  is  screwed  to  the  lower  extremity  of 
the  /  hook,  so  that  the  wire  is  carried  under  the  cross-arm  at  the  point  of 
transposition. 


CHAPTER  XXII 


TELEPHONY.     SIMULTANEOUS  TELEGRAPHY  AND  TELEPHONY 
OVER  THE  SAME  WIRES 

Although  in  long-distance  telephony  metallic  circuits  are  used  exclusively, 
it  is  possible  under  favorable  conditions  to  use  single-line  grounded  circuits 
for  telephoning  over  comparatively  short  distances.  This  fact  is  noted 
here  in  view  of  the  possibilities  in  the  way  of  joining  up  branch-line  grounded 
circuits  to  long-distance  metallic  circuits,  which  will  be  explained  presently. 

Figure  389  shows  theoretically  the  main-line  connections  of  a  grounded- 
line  telephone  circuit,  employing  separate  talking  battery  at  each  station. 
On  grounded  telephone  lines  intermediate  stations  may  be  introduced  as  at 
A,  which  shows  the  series  connection,  or  as  at  B,  which  shows  the  bridging  or 
multiple  connection.  At  each  station  a  50-  to  75-volt,  alternating-current, 


Line 


Line 


Line 


FIG.  389. — Grounded  line  telephone  circuit. 

hand-operated  generator  is  used  to  operate  the  polarized  bells  at  the  various 
stations,  for  the  purpose  of  signaling.  As  the  operation  of  any  generator 
connected  into  the  line  operates  all  of  the  signaling  bells  in  circuit,  each 
station  is  given  a  call.  Where  but  three  or  four  stations  are  located  upon  a 
line,  the  call  for  one  office  may  be  two  short  rings,  for  another  three  short 
rings,  for  the  third  four  short  rings,  and  for  the  fourth  station,  five  short 
rings.  The  single  short  ring,  generally  being  reserved  for  " ring-off"  pur- 
poses. Where  a  larger  number  of  offices  are  located  upon  one  line,  it  is 
necessary  to  form  combination  signals  in  order  to  reduce  to  a  minimum  the 
number  of  signals  required,  thus,  the  call  for  one  office  may  be  two  short 
rings,  a  pause,  and  two  short  rings,  or,  the  signal  "22."  Likewise  other 
offices  may  be  given  signals  such  as  "13,"  "41,"  "21,"  etc. 

The  resistance  of  the  ringer  magnets  used  in  grounded  circuits  when  con- 
nected in  series  is  about  80  ohms,  and  when  connected  in  multiple,  ranges 
from  i;ooo  to  2,500  ohms. 

432 


SIMULTANEOUS  TELEGRAPHY  AND  TELEPHONY         433 


t* 

r~>* 

f 

>l 

ff                    Hj*>t 

1                   1 

X*  J 

f 

*=H                 1 

FIG.  390. — Metallic-circuit  telephone  line. 


r*"         ^   r'          * 


FIG.  391. — Series  telephone  set. 


FIG.  392. — Bridging  telephone  set. 


434  AMERICAN  TELEGRAPH  PRACTICE 

Figure  390  shows  theoretically  the  main-line  connections  of  a  two-wire 
or  metallic  telephone  circuit. 

In  the  metallic  arrangement  it  is  customary  to  connect  intermediate 
offices  in  multiple,  as  shown  at  B,  Fig.  390,  using  2,5oo-ohm  bridging  bells. 

Figure  391  shows  the  wiring  of  a  "series"  telephone  set,  and  Fig.  392, 
the  wiring  of  a  "  bridging"  telephone  set. 

The  two  wires  used  for  metallic  circuit  telephone  operation,  for  satis- 
factory working  must  have  identical  characteristics,  such  as  resistance, 
capacity,  leakage,  and  inductance.  In  practice  slight  variations  are  permiss- 
able  in  any  of  these  factors,  but  the  talking  efficiency  of  the  circuit  is  reduced 
if  considerable  variations  exist.  Where  a  sufficient  number  of  conductors 
of  the  same  gage  are  available  it  is  an  easy  matter  to  effect  proper  balances 
by  transposing  the  conductors  as  explained  in  Chapter  XXI. 

The  current  supplied  to  telephone  transmitters  may  be  derived  from 
primary  batteries  of  the  Edison,  gravity,  Fuller,  LeClanche,  or  dry-cell  types, 
or  from  storage  batteries. 

CONNECTING  GROUNDED  LINES  TO  METALLIC  CIRCUITS 

A  metallic  circuit  and  a  single  grounded  line  may  be  joined  together  by 
connecting  the  two  lines  through  a  repeating  coil  R  as  indicated  in  Fig.  393. 


Line 


Y  _  Z 

?  ? 


FIG.  393.  —  Grounded    line    joined  FIG.  394.  —  Section  of  a  through  telegraph 

to  a  metallic  circuit  through  a  repeat-  wire  serving  as  one  side  of  a  metallic  tele- 

ing  coil.  phone  circuit. 

In  those  cases  where  a  single  grounded  telephone  wire  is  strung  upon  the 
same  pole  line  with  a  through  telegraph  wire  it  is  possible  for  short  distances 
to  use  the  telegraph  wire  as  one  side  of  a  metallic  telephone  circuit  without 
seriously  interfering  with  the  operation  of  either  circuit. 

Figure  394  shows  one  method  of  accomplishing  this.  The  telegraph  wire 
A-B  extends  through  the  stations  at  which  telephones  Y  and  Z  are  located. 
Instead  of  using  an  earth  return  for  the  telephone  circuit,  a  section  of  the 
telegraph  wire  may  be  used  for  the  purpose  by  connecting  the  telephone 
directly  to  the  telegraph  line  as  indicated  in  the  diagram.  The  annexed 
telephone  circuit  forms  a  shunt  to  a  portion  of  the  telegraph  line,  but  owing 
to  the  high  resistance  of  the  telephone  instruments  as  compared  with  the 
resistance  of  the  section  of  telegraph  line  shunted,  comparatively  little  of  the 
telegraph  current  will  be  diverted.  In  fact,  the  joint  resistance  of  the  tele- 


SIMULTANEOUS  TELEGRAPHY  AND  TELEPHONY        435 

phone  circuit  and  that  portion  of  the  telegraph  conductor  used  will  be  less 
than  that  of  the  telegraph  conductor  alone,  reducing  to  that  extent  the  total 
resistance  of  the  telegraph  circuit. 

A  similar  method  of  tying  a  telephone  line  to  a  telegraph  line  is  shown  in 
Fig-  395,  the  connection  being  made  at  each  station  through  condensers  C 
and  C',  which  permit  the  passage  of  the  alternating  current  telephone 
impulses,  but  prevent  the  direct  current  telegraph  impulses  getting  into  the 
telephone  apparatus. 

Figure  396  illustrates  still  another  method  of  utili2ing  a  section  of  a 
through  telegraph  wire  to  form  one  side  of  a  telephone  circuit.  At  station 
Y,  the  junction  of  the  two  windings  of  retardation  coil  K,  is  connected  with 
the  telegraph  line  east,  while  the  outside  terminals  of  the  windings  of  the 
retardation  coil  join  the  telegraph  wire  to  the  telephone  wire  as  shown, 


Y ?  £*JF 

*— *  t  I         .— 

B 


FIG.    395. — Telephone   wire   con-  FIG.  396. — Retardation    coil    method    of 

nected   to    section   of  through  tele-  tying  telephone  lines  to  telegraph  lines, 

graph  wire  through  a  condenser. 

thereby  forming  a  metallic  circuit  between  stations  Y  and  Z  through  the 
windings  of  the  retardation  coil  at  each  station.  At  station  Z  the  tele- 
graph line  west  is  connected  to  the  junction  of  the  two  windings  of  retarda- 
tion coil  K'.  For  telephonic  purposes,  therefore,  a  metallic  circuit  is  formed 
between  stations  Y  and  Z  by  way  of  C-D-E-F. 

A  telegraph  impulse  passing  from  east  to  west  or  vice  versa,  finds  an 
unobstructed  path  through  the  retardation  coils,  due  to  the  fact  that  the 
two  windings  of  the  coils  are  connected  so  that  the  inductive  action  of  one 
coil  neutralizes  that  of  the  other,  that  is,  when  current  passes  through  the 
windings  in  opposite  directions,  as  is  the  case  when  the  current  enters  at  the 
junction  of  the  two  windings. 

While  the  inductive  reactance  of  the  two  windings  of  the  retardation 
coil  to  the  comparatively  slow  telegraph  impulses  is  neutralized,  this  is  not 
the  case  with  the  high  frequency  telephone  currents. 

The  impedance  of  the  coil  to  the  telegraph  current  does  not  much  exceed 
its  ohmic  resistance,  as  the  impedance 

v  R2-\-(2n  nL)2  =  R,  since  the  current  traverses  the  two  windings  in  op- 
posite directions  around  a  common  core.  Obviously  where  hand  telegraph 
signals  are  concerned  the  value  of  n  (frequency)  is  quite  low,  say,  12  or  15 
per  second. 


436 


AMERICAN  TELEGRAPH  PRACTICE 


The  core  of  the  retardation  coil  forms  a  continuous  magnetic  circuit  of 
comparatively  large  physical  dimensions,  which  tends  to  impede  reversal  of 
its  magnetism  when  the  high  frequency  alternating  telephone  currents  tend 
to  reverse  it,  and  as  to  the  telephone  currents  the  two  windings  of  the  coil 
are  connected  in  series,  with  each  winding  acting  as  an  independent  im- 
pedance coil,  while  the  two  windings  are  connected  in  series  the  total  im- 
pedance is  ascertained  by  the  formula: 

V(2R+2R)2+(2nnL+2nnl)z=  V(R)2+(^nL)2.  In  which  the  value 
of  n  may  be  taken  as  1,000,  and  of  L  as  6  (henries). 

It  is  evident,  therefore,  that  the  telephone  currents  are  confined  to  the 
circuit  C-D-E-F,  while  the  telegraph  currents  will  pass  through  the  joint 
circuit  without  entering  the  telephones. 

Line 


Line 


FIG.  397. — Circuits  of  the  repeating-coil  type  of  simplex. 


HHHH 


Metallic  circuits  built  up  as  indicated  in  Figs.  394,  395,  and  396,  should 
be  transposed  in  the  usual  manner  and  for  the  reasons  explained  in  the  pre- 
ceding chapter. 

It  is  apparent,  also,  that  in  any  of  these  arrangements,  while  intermediate 
telephone  circuits  may  be  inserted  by  bridging  the  telephone  sets,  inter- 
mediate telegraph  stations  cannot  be  introduced  without  seriously  interfering 
with  the  operation  of  the  telephone  circuit,  as  in  that  case  the  telegraph 
impulses  would  be  distinctly  heard  in  the  telephone  receivers. 

In  setting  up  such  combination  circuits  the  material  and  resistance  of 
the  wire  used  in  each  side  should  be  the  same. 

THE  SIMPLEX  CIRCUIT 


The  simplex  circuit  arranged  as  shown  in  Fig.  397,  provides  for  tele- 
graphing over  a  circuit  which  is  at  the  same  time  being  used  for  telephony. 


THE'SIMPLEX 


437 


There  are  two  types  of  simplex  apparatus,  one  employing  a  repeating 
coil  and  the  other  a  bridged  impedance,  the  former  is  illustrated  diagram- 
matically  in  Fig.  397,  and  the  latter  in  Fig.  398. 

The  repeating  coil  arrangement  is  not  as  efficient  from  a  telephone 
transmission  standpoint  for  long  lines  as  the  bridged  impedance  arrangement, 
as  the  introduction  of  each  repeating  coil  of  the  usual  type  into  the  line  has 

Line 


Line 


FIG.  398. — Bridged  impedance  coil  type  of  simplex. 

an  effect  equivalent  to  the  introduction  of  i  1/2  miles  of  No.  19  B.  &  S. 
cable  conductor,  or  28  1/2  miles  of  No.  8  B.  W.  G.  open  line.  The  effect 
of  the  bridged  terminal  equipment  of  the  impedance  coil  system  may  be  con- 
sidered as  equivalent  to  1/4  mile  of  cabled  conductor. 

The  following  table  of  equivalents  indicates  the  relative  transmission 
efficiency  of  the  various  gages  and  kinds  of  wire  used: 


Miles  of  line  equiva- 

Conductor 

Pounds  per  mile 

lent  to  i  mile  of 

No.  8  B.  W.  G. 

No.  8  B.  W.  G.,  copper... 

A-2C 

I  .  O 

No.  12  N.  B.  S.  G.,  copper  

M-OO 

173 

0.46 

No.  14  N.  B.  S.  G.,  copper  

IO2 

0.28 

No.  6  B.  W.  G.,  B.  B.,  iron  

573 

o.  19 

No.  8  B.  W.  G.,  B.  B.,  iron  

378 

o.  16 

No.  10  B.  W.  G.,  iron  

2^O 

o.  14 

No.  12  B.  W.  G.,  B.  B.,  iron  

•^  0 

165 

O.II 

No.  14  B.  W.  G.,  B.  B.,  iron  

96 

0.08 

No.  19  B.  &  S.  cable  (0.072  m.f.)  

21 

0.03 

No.  9  B.  &  S.  copper  

2IO 

o  t?4  (est.) 

w  .  3^1-    ^v-oi^.y 

438 


AMERICAN  TELEGRAPH  PRACTICE 


In  Fig.  397,  A  and  B  are  two  telephone  stations  connected  by  a  metallic 
circuit  through  repeating  coils  C  and  C.  Taps  are  taken  from  the  middle 
of  one  side  of  each  coil  to  telegraph  sets  T  and  T',  thence  to  the  telegraph 
main-line  battery  and  ground  at  each  station.  The  two  line  wires  carry 
the  telephone  current  in  opposite  directions,  but,  acting  as  a  joint  circuit 
to  the  telegraph  current,  the  two  line  wires  form  one  side  of  a  ground  return 
telegraph  circuit. 

By  noting  the  direction  of  the  windings  around  the  continuous  iron  core 
of  the  repeating  coil,  it  will  be  apparent  that  the  telegraph  currents  flow  in 


FIG.  399. — Intermediate  telephone  stations  on  simplex  circuit. 

opposite  directions  around  the  core,  the  action  of  one  winding  neutralizing 
the  inductive  effect  of  the  other,  and  if  the  electrical  characteristics  of  the 
two  line  wires  are  the  same,  the  telegraph  impulses  will  not  affect  the  tele- 
phone receivers. 

The  retardation  coil  type  .of  simplex  circuit  shown  theoretically  in  Fig. 
398  has  two  terminal  telephone  stations  A  and  B  connected  to  the  two  line 
wires  forming  the  metallic  circuit  through  4-m.f.  condensers.  The  high- 
frequency  alternating  talking  current  readily  passes  through  the  condensers, 
while  the  slowly  pulsating  direct-current  Morse  impulses  cannot  enter  the 


Telephone 


Exchange 


Telegraph 
FIG.  400. — Simplex  circuit  connected  through  an  intermediate  telephone  exchange. 

condenser  circuit  containing  the  telephones.  The  retardation  coil  bridged 
across  the  line  wires  at  each  terminal  station  has  two  5oo-ohm  windings 
around  an  iron  core,  giving  the  coil1  a  very  high  impedance  to  alternating 
currents.  At  the  junction  of  the  windings  of  the  two  coils  the  Morse  circuit 
is  tapped  off,  leading  to  relay,  key,  battery  and  ground. 

Inasmuch  as  the  resistance  and  reactance  of  the  coils  and  of  the  two 
line  wires  forming  each  side  of  the  circuit  are  identical,  the  current  divides 
equally  in  the  two  branches  of  the  circuit,  and  as  the  difference  of  potential 
at  any  point  along  the  line  is  the  same  in  each  wire,  it  is  evident  that  inter- 


PHANTOM  TELEPHONE  CIRCUITS 


439 


mediate  telephone  stations  may  be  bridged  across  the  two  line  wires.     See 

Fig-  399- 

In  those  cases  where  the  line  is  run  through  an  intermediate  telephone 
exchange,  repeating  coils  are  connected  into  the  metallic  circuit  on  each 


FIG.  401. — Intermediate  telegraph  station  connected  into  a  simplex  circuit. 

side  of  the  exchange  switchboard  as  indicated  in  Fig.  400,  the  telegraph 
circuit  being  completed  through  the  exchange  by  means  of  a  wire  connecting 
the  middle  point  of  each  retardation  coil  as  shown. 

Figure  401  shows  a  simplex  circuit  with  an  intermediate  telegraph  station. 


FIG.  402. — Intermediate  telephone  and  intermediate  telegraph  station  connected 
'  into  a  simplex  circuit. 

Figure  402  shows  a  simplex  circuit  with  an  intermediate  telephone 
station  and  an  intermediate  telegraph  station  inserted. 

PHANTOM  TELEPHONE  CIRCUITS 

The  phantom  is  an  arrangement  by  which  three  telephone  circuits  may  be 
obtained  from  two  pairs  of  line  wires.  The  combination  is  referred  to  as 
consisting  of  two  physical  circuits  and  one  phantom  circuit. 


FIG.  403. — Phantom  telephone  circuit. 

A  and  B,  Fig.  403,  are  two  stations  connected  by  a  metallic  circuit,  as 
also  are  stations  C  and  D.  A  repeating  coil  is  inserted  at  each  end  of  each 
metallic  circuit  as  shown  in  the  diagram.  At  each  station  the  two  line  wires 


440  AMERICAN  TELEGRAPH  PRACTICE 

from  a  third  telephone  set  are  connected  to  the  middle  of  each  repeating 
coil,  thereby  employing  the  two  wires  of  each  metallic  circuit  as  one  side  of 
an  additional,  or  phantom  circuit. 

Special  forms  of  transposition  of  the  four  wires  are  required  in  order  to 
prevent   cross-talk.     Fig.   404   shows   various   transposition   arrangements 


FIG.  404. — Special  forms  of  line  transposition  necessary  where  phantom  circuits 

are  made  up. 

of  the  wires  of  the  physical  circuits  and  of  the  two  sides  of  the  phantom 
circuit. 

Intermediate  stations  may  be  inserted  in  each  physical  circuit,  and  there 
will  be  no  interference;  provided  a  correct  balance  is  maintained  between 
the  two  wires  forming  the  circuit. 


K1 


FIG.  405. — Intermediate  telephone  station  on  phantom  circuit. 

Figure  405  shows  the  necessary  connections  for  inserting  an  inter- 
mediate station  into  the  phantom  circuit.  Retardation  coils  K  and  K'  are 
bridged  across  the  physical  circuits.  From  the  center  of  each  of  these  coils 
a  tap  is  taken  to  one  side  of  a  condenser,  the  other  terminal  of  which  is 


PHANTOM-SIMPLEX  CIRCUITS  441 

connected  with  the  telephone  set  to  be  bridged  into  the  phantom  circuit. 
The  presence  of  the  retardation  coil  in  the  physical  circuit  does  not  appreci- 
ably interfere  with  the  talking  efficiency  of  that  circuit  as  the  inductive 
resistance  of  the  coil  to  high-frequency  currents  tending  to  enter  it  at  one 
end  and  leave  at  the  other  acts  to  prevent  the  currents  circulating  in  the 
physical  circuit  from  being  shunted.  The  phantom  currents,  on  the  other 
hand,  traveling  in  the  same  direction  in  wires  i  and  2,  and  3  and  4,  enter  the 
retardation  coils  at  both  ends  at  the  same  instant—  the  only  opposition 
presented  to  the  incoming  currents  being  that  of  non-inductive  resistance. 
The  out-going  currents  from  the  intermediate  phantom  station  pass  through 
the  windings  of  the  retardation  coils  in  opposite  directions,  again  encounter- 
ing only  non-inductive  resistance. 

THE  PHANTOM  SIMPLEX  CIRCUIT  ^ 

In  combining  circuits  to  provide  phantom  simplex  operation,  there  is  a 
certain  degree  of  loss  in  the  efficiency  of  telephone  transmission,  and  the  satis- 
factory operation  of  the  system  requires  that  in  every  case  the  wires  em- 


o 


Telegraph 

o 


FIG.  406.  —  Phantom  simplex  circuit. 

ployed  in  forming  the  different  sides  of  the  circuit  must  be  of  the  same  com- 
position and  of  the  same  resistance. 

Figure  406  illustrates  theoretically  the  manner  in  which  a  telegraph 
circuit  is  superimposed  upon  a  phantom  circuit  already  serving  as  two  tele- 
phone circuits.  Intermediate  telephone  stations  may  be  connected  into 
either  physical  circuit  or  into  the  phantom  circuit  without  causing  inter- 
ference. In  the  case  of  the  phantom  intermediate  connection  it  is  necessary 
to  use  condensers  as  indicated  in  Fig.  405. 

It  will  be  apparent  that  when  one  side  of  a  telegraph  circuit  consists  of 
four  line  wires,  as  in  the  phantom  simplex  arrangement,  the  resistance  of  the 
circuit  thus  made  up  will  be  comparatively  low  and  (as  is  also  the  case  with 
the  ordinary  simplex  arrangement)  the  telegraph  circuit  being  grounded  at 
each  terminal  station,  some  difficulty  is  likely  to  be  experienced  due  to  earth 
currents.  The  remedy  is  to  insert  artificial  non-inductive  resistance  at  one 
or  both  of  the  telegraph  stations. 

In  arranging  phantom  circuits,  cabled  conductors  should  be  avoided  as 


442 


AMERICAN  TELEGRAPH  PRACTICE 


far  as  possible,  although  if  "  double- twisted "  pairs  are  used,  reasonably 
efficient  operation  is  possible. 

THE  COMPOSITE  CIRCUIT 

In  arranging  for  composite  operation  it  is  well  to  remember  that  iron  wire 
is  much  inferior  to  copper  wire  of  the  same  size  when  used  for  telephone 
purposes,  and  also  that  cabled  conductors  are  much  less  efficient  than  open 
conductors  suspended  on  poles  in  the  usual  manner.  Where  the  employ- 
ment of  cabled  conductors  is  unavoidable,  from  a  transmission  standpoint 
paper-insulated  conductors  are  considerably  more  efficient  than  rubber- 
insulated  wires;  that  is,  for  wires  of  the  same  size.  This  is  owing  to  the  rela- 
tively high  electrostatic  capacity  of  rubber-insulated  conductors. 

In  view  of  the  widely  different  conditions  encountered  it  is  difficult  to 
lay  down  d^nite  rules  applicable  to  all  proposed  installations  of  composite 
apparatus,  so  far  as  the  length  of  line  and  possible  number  of  stations  in 
circuit  are  concerned. 

Except  in  those  cases  where  composite  service  has  been  contemplated  in 
the  original  construction  of  the  line  and  stringing  of  the  wires,  .each  particular 
telegraph  line  or  telephone  line  must  be  considered  separately  before  a  correct 
determination  can  be  made  in  regard  to  its  adaptability  for  composite  service. 

THE  GROUNDED  LINE  COMPOSITE 

Figure  407  shows  the  circuits  of  a  grounded  composite  installation  at  a 
terminal  office  and  at  an  intermediate  telegraph  office.  The  direct-current 


Line 


FIG.  407. — The  grounded  composite. 

impulses  from  the  telegraph  battery  B  have  an  uninterrupted  path  via  the 
key  and  relay  at  the  terminal  station,  through  the  retardation  coil  $-/,,  over 


COMPOSITE  CIRCUITS  443 

the  line  wire,  through  the  Morse  relay  at  the  intermediate  station,  and  on  to 
the  distant  terminal  station,  in  the  same  manner  passing  through  any  other 
intermediate  telegraph  offices  inserted  between  the  two  terminal  stations. 

The  presence  of  the  condenser  C,  prevents  the  telegraph  impulses  from 
being  shunted  to  earth  through  the  telephone  apparatus,  while  the  presence 
of  the  condenser  C  connected  around  the  Morse  relay  at  the  intermediate 
telegraph  station  provides  a  path  for  the  high-frequency  alternating  telephone 
currents  past  that  station,  whether  the  Morse  key  K  is  open  or  closed. 

THE  HOWLER  SIGNAL 

In  operating  call-bell  signals  over  the  simplex  circuit  (Fig.  398)  the  alter- 
nating currents  produced  by  the  generator  pass  over  the  line  in  the  same  man- 
ner as  the  talking  currents,  and,  ordinarily  no  difficulty  is  experienced  pro- 
vided high  power  generators  and  condensers  having  a  large  enough  capacity 
are    used    in    connection    therewith.     In    many 
modern  telephone  exchanges  one  side  of  the  ring- 
ing  generator  is   grounded.     Obviously   such   an 
arrangement   cannot  be   used  for   signaling   over 
simplex  circuits  without  causing  chattering  of  the 
armatures  of  the  Morse  relays  while  the  signaling 
impulses  are  being  sent  over  the  line.     It  is  neces- 
sary, therefore,  where  the  retardation  coil  type  of 
simplex  is  used  to  provide   a  metallic  generator     FIG<  408.— The  howler, 
circuit. 

In  the  repeating  coil  type  of  simplex  the  grounded  generator  may  be 
employed,  as  the  two  windings  of  the  coil  have  no  direct  electrical  connection 
with  each  other. 

In  signaling  over  composited  lines,  a  " howler,"  Fig.  408,  is  generally 
used. 

This  instrument  consists  of  a  special  form  of  telephone  receiver  equip- 
ped with  a  resonating  megaphone.  The  diaphragm  is  operated  by  the  high- 
frequency  signaling  currents  produced  by  an  induction  coil  fitted  with  an 
interrupter,  as  at  7,  Fig.  407 — depressing  the  button  b  closes  the  primary 
circuit  of  the  induction  coil  connected  with  a  source  of  direct  current,  causing 
the  vibrator  to  act,  resulting  in  sending  out  powerful  high-frequency  signaling 
currents  over  the  line  to  actuate  the  howler  connected  into  the  distant 
telephone  set. 

The  sound  emitted  by  the  howler  may  be  varied  by  adjusting  the  position 
of  the  diaphragm  relatively  to  the  electromagnets. 

THE  METALLIC  CIRCUIT  COMPOSITE 

In  all  cases  where  it  is  desired  to  maintain  telephone  service  over  long 
distances,  say  from  100  to  1,000  miles,  the  metallic  circuit  is  indispensable. 


444 


AMERICAN  TELEGRAPH  PRACTICE 


Conn  pos 


No   "in-termedicrt<3  phones  bridged. 
FlG.  409. 


i       T 


~-p- 


- 


TbrougK  "belephone,  inter,  telegraph. 

FIG.  410. 


"""         .  T.I. 


r5 


tf 

Separat-e  felepViones  an^i       »    "*" 
Vhrough  or  separate  -telegraph 

FlG.   411. 


ITT^x-tf 


INTERMEDIATE  COMPOSITE. 

FIG.  412. 


COMPOSITE  CIRCUITS 


445 


1 


1 

111 

_       tt>~ 

ToC 

llh 

I 
A                                                      B 

-u™^- 
=  6MF 

—  'WOOWCTOCTHI  —  < 

/          SK       £ 

-8MF 

5L 
--8MF 

£MF                             £MF 

ro  Phone  To  Phor 

J~^00^0°"\_ 

\ 
—  ^fiAMMMitHI  —  ' 
^6MF             5K       I  _ 

1 

76  '  V-^mmS 

-6MF 
ToD 

JMF                             IMF 

-8MF 

--8MF 
5L 

FIG.  413. — Complete  connections  of  the  composite  circuit,  showing  condenser  capacities- 


^m^ 

Inductance  4     SL-Co'il 

to  bcvlcince  =i=                 J 

inductance  of  JAdjustoble 

^instr-umen'ts  o.t  -W Condenser' 


"Distant  Station 


'  -  5-^:  GOILS  -  so  OHMS 


C0MF0SITE  CIRCUIT. 


FIG.  414. — Terminal  office  instrument  and  main  switchboard  connections  where  each 
side  of  the  telephone  circuit  is  used  for  a  telegraph  duplex. 


446 


AMERICAN  TELEGRAPH  PRACTICE 


The  organized  apparatus  of  the  metallic  circuit  composite  makes  possible 
the  employment  of  each  side  of  the  telephone  circuit  as  a  telegraph  circuit. 

Figure  409  shows  the  schematic  circuit  arrangements  of  a  composited 
line  employing  the  two  line  wires  as  a  metallic  telephone  circuit,  and  each 
line  wire  as  a  separate  grounded  telegraph  circuit. 

Figure  410  shows  the  theoretical  arrangement  of  circuits,  where  the  two 
line  wires  are  used  for  through  telephone  service  and  where  each  line  wire  is 
used  for  telegraph  service  between  two  terminal  stations  including  an  in- 
termediate telegraph  station  on  each  line. 

Figure  411  shows  a  similar  arrangement,  providing  for  separate  telephone 
circuits  in  both  directions  from  an  intermediate  office,  and  for  either  through 


These  Cords  to  be  kept 
inSpringJacff,  with 
Dotted  side  out  \ 


0     0 


5LCoil,300hms  ~  5LCoil,300hms 


5L  Coil,  50  Ohms 
ItoSMF 


FIG.  415. — Instrument  binding-post  connections  at  a  terminal  office. 
Composite  circuit. 


or  separate  telegraph  service.  Fig.  412  shows  the  switching  arrangements 
at  the  intermediate  office  which  provide  for  cutting  any  of  the  circuits,  and 
for  connecting  them  for  through  service  between  terminal  stations. 

Figure  413  shows  with  fewer  lines  the  actual  arrangement  of  circuits  at 
the  intermediate  office.  Telephone  service  is  maintained  between  stations 
A  and  B,  while  telegraph  service  is  maintained  over  one  wire  between  station 
A  and  a  distant  station  C,  and  over  the  other  wire  between  station  A  and  a 
distant  station  D.  In  this  diagram  the  condenser  values  found  necessary 
in  a  particular  case  are  noted. 

Figure  414  shows  the  required  instrument  and  main  switchboard  con- 


REPEATING  COILS  447 

nections  where  duplex  telegraph  service  is  maintained  over  each  of  the  two 
wires  used  in  forming  the  metallic  telephone  circuit. 

Figure  415  shows  the  actual  binding-post  connections  of  the  retardation 
coils,  condensers,  and  telephone  pin-jacks.  The  apparatus  is  connected  to 
the  two  line  wires  by  means  of  the  cords  bearing  on  one  end  double  plugs 
and  on  the  other  double  wedges,  the  plugs  being  inserted  in  the  pin- jacks, 
and  the  wedges  in  the  spring- jacks  of  the  main-line  switchboard  as  indicated 
in  the  diagram. 

REPEATING  COILS  AND  RETARDATION  COILS  USED  IN  SIMPLEX  AND 
COMPOSITE  CIRCUITS 

Figure  416  shows  a  view  of  the  form  of  repeating  coil  known  as  37~^4. 
These  coils  have  two  primary  windings  of  35  ohms  each  and  two  secondary 
windings  of  35  ohms  each.  The  coils  are  used  in  phantom  toll  circuits  and 


FIG.  416. — 37:A  repeating  coil. 

in  simplex  circuits.  The  size  of  the  baseboard  upon  which  the  coil  is  mounted 
is  ii  in.  X  8  5/8  in.  Fig.  417  shows  the  terminal  markings  and  circuit 
connections  of  the  3*j-A  type  coil  when  used  for  simplex  working. 

Figure  418  shows  the  terminal  connections  of  the  $-N  type  retardation 
coil.  This  coil  has  four  windings  of  250  ohms  each.  Total  resistance  1,000 
ohms  when  measured  with  direct  current.  The  inductance  of  the  coil  with 
windings  in  series  is  507  henries,  and  with  the  windings  in  multiple  3.1 
henries. 

The  $-K  type  retardation  coil  has  two  windings  of  15  ohms  each.  Total 
resistance  measured  with  direct  current  30  ohms.  The  effective  resistance 
of  the  coil  to  alternating  currents  having  a  frequency  of  1,000  p.p.s.  is 
3,000  ohms  with  the  windings  in  series  inductively.  The  inductance  with 
both  windings  in  series  inductively  is  3.1  henries. 

The  5-1,  type  retardation  coil  has  two  windings  of  25  ohms  each.  Total 
resistance  measured  with  direct  current  is  50  ohms.  The  effective  resistance 
measured  with  alternating  current  of  1,000  p.p.s.  is  2,500  ohms  with  both 
windings  in  series  inductively.  With  both  windings  in  series  opposing  each 


448 


r  AMERICAN  TELEGRAPH  PRACTICE 


other,  the  effective  resistance  is  700  ohms.  The  inductance  of  the  coil  with 
both  windings  in  series  inductively  and  measured  with  alternating  current 
having  a  frequency  of  1,000  p.p.s.  is  4.8  henries,  and  under  the  same  condi- 
tions of  current  writh  both  windings  in  series  opposing  inductively  3  henries. 


/  =  IP. 
2=  Of? 
3=  75. 
4=  05. 

FIG.   417. — Terminal  markings  and 
connections  of  the  3  7- A  coil. 


FIG.  418. — Terminal  markings  and 
connections  of  5-N  type  retardation 
coil. 


The  5- £7  type  coil  (which  is  of  the  same  construction  as  the  37-^  type  of 
coil)  used  in  connection  with  the  Western  Union  standard  quadruplex  has 
two  windings  of  500  ohms  each.  Total  resistance  1,000  ohms  measured 
with  direct  current.  The  inductance  with  both  windings  in  series  is  584 
henries  and  with  the  windings  in  multiple  3.84  henries. 


CHAPTER  XXIII 


SPECIFICATIONS  FOR  COPPER  AND  IRON  WIRE,  AERIAL, 
UNDERGROUND,  SUBMARINE,  AND  OFFICE  CABLES 

SPECIFICATION  FOR  HARD -DRAWN  COPPER  WIRE 
ROLLING  AND  DRAWING 

The  copper  bars,  before  rolling,  shall  be  free  from  defects,  and  each  coil 
shall  be  in  one  continuous  length  without  joints. 

All  wire  furnished  under  this  specification  shall  be  perfectly  cylindrical, 
uniform  in  size  and  quality,  free  from  flaws,  splits,  kinks  and  other  defects. 
The  manufacturer  shall  cut  off  before  inspection  sufficient  length  from  each 
end  of  every  coil  to  insure  freedom  from  defects. 

MECHANICAL  AND  ELECTRICAL  REQUIREMENTS 


Diame- 
ter mils 

Weight  per  mile  pounds 

Breaking  weight 
pounds 

Minimum 

Maxi- 

B. &  S. 
gage 

average 
must 

Maxi- 

Mini- 

Average 
must 

Mini- 

Lot 
must 

percentage 
elongation 
allowed  in 

mum 
mileohm 
allowed 

not 
exceed 

mum 
allowed 

mum 
allowed 

not 
exceed 

mum 
allowed 

average 
at  least 

5  feet 

at  60°  F. 

7 

144 

337 

328 

332-5 

1,020 

1,050 

.09 

• 

7* 

137 

305 

296 

300.5 

930 

950 

.07 

8 

128.5 

268 

260 

264 

820 

840 

.06 

9 
9i 

114 
104 

212 
I76 

204 
169 

208 
172-5 

,    650 
540 

670 

555 

.02 
.00 

894.7 

10 

IO2 

169 

163 

166 

520 

535 

.00 

B.  W.  G. 

8 

165 

439 

43i 

435 

1,328 

i,378 

1.14 

TESTING  AND  APPARATUS 

The  mechanical  and  electrical  tests  shall  be  made  in  a  manner  and  with 
apparatus  approved  by  the  electrical  engineer  of  the  telegraph  company. 

Tests  are  to  be  applied  to  sample  pieces  of  wire,  cut  from  not  less  than 
one-tenth  of  the  number  of  bundles,  as  selected  by  the  inspector  of  the 
telegraph  company  from  the  whole  lot  of  wire  under  inspection. 

Samples  selected  at  random  by  the  inspector  shall  be  used  for  electrical 
measurement. 

29  449 


450  AMERICAN  TELEGRAPH  PRACTICE 

REJECTIONS 

The  inspector  may  reject  any  wire  which  does  not  meet  the  foregoing 
mechanical  and  electrical  requirements;  and,  if  such  rejections  include  the 
entire  lot,  the  expenses  of  inspection  shall  be  borne  by  the  manufacturer. 

Any  imperfect  material  or  work  discovered  before  acceptance  of  the  wire 
shall  be  replaced  or  corrected  upon  demand  of  the  telegraph  company, 
even  if  such  imperfections  were  not  apparent  during  inspection  of  the  samples 
selected. 


COILS 

Each  coil  to  be  a  continuous  length  without  joint  or  splice,  and  to  have 
an  inside  diameter  of  from  20  to  22  in. 

Under  direction  of  the  inspector,  a  lead  seal  of  the  telegraph  company 
shall  be  attached  to  the  inside  of  each  accepted  coil  with  a  soft  copper  wire 
fastener.  Such  lead  seals  and  wire  fasteners  will  be  provided  by  the  tele- 
graph company.  All  other  attachments  to  be  made  with  strong  twine. 

Weight  of  Coils. — The  length  and  weight  of  wire  in  each  coil  of  the  same 
gage  to  be  as  nearly  equal  as  practicable,  and  the  weight  to  be  determined 
by  the  following: 

Ninety-five  per  cent,  of  the  bundles  of  gage  No.  9  B.  &  S.  (.114  in.)  or 
smaller,  to  weigh  not  more  than  220  lb.,  nor  less  than  190  Ib.  each.  Five 
per  cent,  of  low-weight  coils  will  be  accepted,  the  minimum  weight  to  be 
125  lb. 

Ninety-five  per  cent,  of  the  bundles  of  gages  larger  than  No.  9  B.  &  S. 
to  weigh  not  more  than  220  lb.,  nor  less  than  150  lb.  each.  Five  per  cent, 
of  low- weight  coils  will  be  accepted,  the  minimum  weight  to  be  125  lb. 

Each  coil  shall  be  securely  bound  with  at  least  four  separate  wrappings 
of  strong  twine,  and  shall  afterward  be  so  protected  by  wrappings  of  burlap 
that  there  will  be  no  danger  of  mechanical  injury  in  transportation.  Each 
coil  shall  have  the  weight,  gage  and  length  of  wire  plainly  and  indelibly 
marked  on  two  strong  tags,  one  of  which  shall  be  attached  to  the  coil  inside 
of  the  burlap,  and  the  other  outside  of  the  burlap.  Upon  the  inside  tag 
shall  be  marked  the  order  number  of  the  telegraph  company  and  the  date  of 
inspection. 

SPECIFICATION  FOR  GALVANIZED  IRON  WIRE 

All  wire  furnished  under  this  specification  shall  be  perfectly  cylindrical, 
uniform  in  size  and  quality,  free  from  flaws,  splits,  kinks  and  other  defects. 
The  manufacturer  shall  cut  off  before  inspection  sufficient  length  from  each 
end  of  every  coil  to  ensure  freedom  from  all  such  defects. 


SPECIFICATIONS  FOR  COPPER  AND  IRON  WIRE        451 


Testing  Apparatus. — The  mechanical  and  electrical  tests  shall  be  made  in  a 
manner  and  by  apparatus  approved  by  the  electrical  engineer  of  the  tele- 
graph company. 

The  wire  must  meet  the  requirements  of  the  following  table. 

TABLE  OF  MECHANICAL  AND  ELECTRICAL  REQUIREMENTS 


Breaking   weight 
pounds 

Twists  in  6  in. 

Per- 

Maxi- 
mum 

Birming- 
ham 
gage 

Diame- 
ter mils 

Weight 
per  mile 
pounds 

Lot 
must 

Mini- 
mum 

Lot 
must 

Mini- 
mum 

centage 
elonga- 
tion 

mile 
ohm 
allowed 

average 
at  least 

allowed 

average 
at  least 

allowed 

at  60°  F. 

No. 

4 

238 

787 

2,200 

2,120 

15 

12 

15 

5 

220 

673 

1,880 

1,820 

16 

13 

i5 

6 

203 

573 

i,  600 

1,550 

18 

15 

15 

7 

180 

45o 

1,260 

I,2IO 

20 

i7 

14 

>   4,700 

8 

165 

378 

i,  060 

I,O2O 

22 

18 

13 

9 

148 

305 

860 

820 

25 

21 

12 

10 

134 

250 

700 

670 

25 

21 

12 

Tests  are  to  be  applied  to  sample  pieces  of  wire  cut  from  not  less  than  one- 
tenth  of  the  number  of  bundles  as  selected  by  the  inspector  of  the  telegraph 
company  from  the  whole  lot  of  wire  under  inspection. 

The  twist  tests  to  be  made  by  properly  gripping  the  sample  wire  at  the 
ends  by  two  vises  whose  jaws  are  6  in.  apart  at  the  gripping  points,  and 
causing  one  vise  to  revolve  at  right  angles  to  the  wire  at  a  uniform  speed 
of  about  one  revolution  per  second.  The  twists  to  be  reckoned  by  the 
number  of  complete  revolutions  made  by  the  revolving  vise  before  the  wire 
breaks. 

Test  pieces  taken  at  random,  shall  be  used  for  electrical  measurement,  and 
the  resistance  calculated  to  60°  F.  in  international  ohms,  using  a  temperature 
coefficient,  for'  iron  of  0.0029  ohm  per  degree.  The  electrical  resistance  of 
the  wire  in  ohms  per  mile  at  a  temperature  of  60°  F.  must  not  exceed  the  quo- 
tient obtained  by  dividing  the  constant  number  4,700  by  the  weight  of  the 
wire  in  pounds  per  mile.  The  inspector  may  measure  the  electrical  resist- 
ance of  as  many  samples  as  he  desires  to  test. 

If  upon  test  it  be  found  by  the  inspector  that  the  requirements  for  the 
electrical  or  mechanical  properties  of  the  wire,  or  for  the  finish,  are  not 
fulfilled  when  the  wire  is  offered  for  acceptance,  the  expense  of  all  tests  made 
by  said  inspector  on  such  defective  wire  shall  be  borne  by  the  manufacturer. 


452 


AMERICAN  TELEGRAPH  PRACTICE 


GALVANIZING 

All  wire  must  be  thoroughly  galvanized.  Samples  of  the  wire  under 
inspection  shall  be  dipped  into  a  solution  of  sulphate  of  copper,  saturated  at 
60°  F.  and  allowed  to  remain  for  one  minute,  when  they  are  to  be  withdrawn, 
washed  and  wiped  clean.  The  galvanizing  shall  admit  of  the  process  four 
times  without  any  signs  of  a  reddish  deposit  upon  the  wire. 

Samples  shall  bear  coiling  around  a  cylindrical  bar,  twelve  times  the  di- 
ameter of  the  sample  without  any  signs  of  the  zinc  flaking  or  peeling  off. 

COILS 

Each  coil  shall  be  of  a  continuous  length  and  must  not  contain  more  than 
one  splice  which  must  be  well  soldered. 

The  inside  diameter  of  the  coil  to  be  from  20  to  22  in. 

Under  direction  of  the  inspector,  a  lead  seal  of  the  telegraph  company 
shall  be  attached  to  the  inside  of  each  accepted  coil  with  a  wire  fastener. 
Such  lead  seals  and  wire  fasteners  to  be  provided  by  the  telegraph  company. 

WEIGHT   OF   COILS 

The  length  of  wire  in  each  coil  of  the  same  gage  to  be  as  nearly  equal  as 
practicable,  and  to  be  determined  by  the  following: 

No.  4  B.  W.  G.  shall  contain  4  coils  per  mile. 

No.  5  B.  W.  G.  shall  contain  3  coils  per  mile. 

No.  6  B.  W.  G.  shall  contain  3  coils  per  mile. 

No.  7  B.  W.  G.  shall  contain  2  coils  per  mile. 

No.  8  B.  W.  G.  shall  contain  2  coils  per  mile. 

No.  9  B.  W.  G.  shall  contain  2  coils  per  mile. 

No.  10  B.  W.  G.  shall  contain  i  coil   per  mile. 

Each  coil  shall  be  securely  bound  with  four  strong  binding  wires,  the  joints 
of  these  binding  wires  to  be  inside  the  coil.  Each  coil  shall  have  its  weight 
plainly  and  indelibly  marked  on  a  strong  tag  which  shall  be  firmly  attached 
to  the  inside  of  the  coil. 

SPECIFICATIONS  FOR  STRANDED  GALVANIZED  STEEL  WIRE 


Gage 
B.W.G. 

Diameter 
wire 

Diameter 
strand 

Lay  in 
inches 

Breaking 
weight 

Maximum 
elongation 
24  in. 

Minimum 
elongation 
24  in. 

Pounds 
per 

100  ft. 

8 

0.165 

i 

| 

4!              11,000 

20 

ii 

52 

12 

o.  109 

& 

3^ 

4,860 

18 

ii 

22 

14 

0.083 

\ 

3 

3,050 

17 

9 

13 

16 

0.065 

A 

2 

2,000 

15 

9 

8 

SPECIFICATIONS  FOR  AERIAL  CABLE  453 

INITIAL  STRAIN 

No  piece  of  wire  under  test  shall  be  subjected  to  more  than  10  per  cent,  of 
its  required  breaking  weight  before  its  elongation  is  considered. 

GALVANIZING 

Each  wire  must  be  thoroughly  galvanized.  Samples  of  the  wire  under 
inspection  shall  be  dipped  into  a  solution  of  sulphate  of  copper,  saturated  at 
60°  F.  and  allowed  to  remain  for  one  minute,  when  they  are  to  be  withdrawn, 
washed  and  wiped  clean.  The  galvanizing  shall  admit  of  this  process  four 
times  without  any  signs  of  a  reddish  deposit  upon  the  wire.  Samples  must 
bear  coiling  around  a  cylindrical  bar  twelve  times  the  diameter  of  the  sample, 
without  any  signs  of  the  zinc  flaking  or  peeling  off. 

SPECIFICATION  FOR  AERIAL  TWISTED  PAIR  (RUBBER  COMPOUND 
DIELECTRIC)  CABLE 

All  conductors  to  be  of  No.  14  B.  &  S.  (64  mils  diameter)  thoroughly 
annealed  copper,  98  per  cent,  pure,  according  to  Matthiessen's  standard, 
equal  in  strength,  finish,  and  pliability  to  the  best  market  grade,  well  tinned 
and  uniformly  coated  to  a  diameter  of  158  mils  with  a  high-grade  rubber  per- 
manent insulating  compound,  which  shall  adhere  closely  to  the  wire,  and  which 
shall  not  deteriorate  under  ordinary  conditions. 

Each  insulated  conductor,  before  being  laid  up  into  cable  form,  must  have 
its  dielectric  subjected  in  water,  after  24  hours  immersion,  to  a  strain  of  not 
less  than  1,000  volts  alternating  current  between  the  conductor  and  the  water, 
applied  for  one  minute  from  a  suitable  generator  or  transformer;  and  must 
show  while  in  the  tank,  after  such  immersion,  an  insulation  of  not  less  than 
300  megohms  per  mile  at  60°  F.,  with  not  less  than  100  volts  applied  for  one 
minute.  Test  to  be  made  by  standard  testing  instruments  in  the  presence 
of  an  inspector  of  the  telegraph  company. 

All  conductors  for  test,  either  in  coils  or  reels,  must  have  tags  securely 
attached,  giving  in  plain  figures  the  coil  or  reel  numbers,  the  number  of  feet 
in  each  coil  or  reel,  the  gage  of  wire,  and  diameter  of  insulation;  and  such 
coils  must  so  far  as  practicable  be  in  uniform  lengths  corresponding  to  the 
length  of  the  cable. 

Each  insulated  conductor  in  the  cable  must  be  protected  by  a  closely 
woven  cotton  braid  of  not  less  than  15  mils  thickness,  thoroughly  saturated 
with  a  compound  which  is  not  soluble  in  water,  which  does  not  act  injuriously 
upon  the  permanent  insulating  compound,  braid  or  tape,  and  which  is  not 
objectionable  to  handle. 

The  two  wires  of  a  pair  shall  be  twisted  together,  the  length  of  the  lay  not 
to  exceed  6  in. 


454  AMERICAN  TELEGRAPH  PRACTICE 

One  condcutor  of  each  pair  and  one  pair  in  each  layer  to  be  corded  for 
tracing. 

The  wires  in  each  length  shall  be  each  of  one  piece  and  free  from  joints. 

The  twisted  pairs  shall  be  laid  up  into  a  cylindrical  core  with  the  layers 
in  reverse  directions. 

Each  pair  of  wires  to  be  laid  up  with  cushioning  strands  of  saturated  jute 
yarn  of  proper  size. 

The  cable  must  be  wrapped  over  all  with  flexible  cotton  tape  of  first-class 
quality,  saturated  with  first-class  weatherproof  compound.  The  tape  must 
not  be  less  than  20  mils  thick,  must  have  a  lap  of  one-half  its  width,  and  firm 
adherence  where  lapped,  so  that  it  will  not  readily  come  apart.  Over  this 
the  cable  must  have  a  durable  protection  of  circular  loom,  braid,  or  tape, 
covering  acceptable  to  the  telegraph  company,  thoroughly  saturated  with  the 
aforesaid  compound. 

The  finished  cable  must  not  be  sticky  or  objectionable  to  handle. 

All  cable  made  up  as  above,  prior  to  shipment  from  factory,  and  after 
being  placed  upon  reels,  must  have  each  length  again  tested  for  insulation 
by  the  inspector  of  the  telegraph  company;  and  each  conductor  under  test 
must  show  an  insulation  (when  all  of  the  other  conductors  of  the  length  are 
grounded)  of  not  less  than  500  megohms  per  mile  at  60°  F.,  with  not  less 
than  100  volts  applied  for  one  minute  in  the  usual  manner.1  The  conductors 
of  the  completed  cable  must  also  be  tested  for  continuity,  and  the  inspector 
shall  make  such  tests  for  capacity  and  conductivity  as  he  thinks  advisable. 

The  contractor  will  be  required  to  'furnish  a  table  of  coefficients  of  the 
resistance  of  the  dielectric,  showing  its  decrease  above  and  its  increase  below 
60°  F.,  within  the  limits  of  variation  of  temperature  to  which  the  cable 
may  be  subjected  during  test. 

The  reels  upon  which  the  cable  is  shipped  must  be  strong  and  well  pro- 
tected, and  the  cable  neatly  wound  thereon  with  both  ends  so  arranged  that 
tests  of  the  conductors  on  the  reels  may  readily  be  made. 

A  tag  must  be  securely  fastened  to  each  reel,  upon  which  the  contractor 
must  record  the  exact  number  of  feet  from  end  to  end  of  the  cable  upon  the 
reel,  the  number  of  conductors  in  the  cable,  and  the  date  of  shipment  to  the 
telegraph  company  from  the  contractor's  factory. 

The  contractor  must  give  the  usual  guarantee  that  the  cable  will  remain 
in  good  condition  for  one  year  after  delivery,  provided  it  is  not  used  for 
currents  of  over  one  ampere,  or  having  an  electromotive  force  of  over  500 
volts;  and  must  agree  to  repair  or  to  reimburse  the  company  for  any  expendi- 
tures incurred  in  repairing  defects  that  may  appear  during  that  period,  not 
caused  by  mechanical  or  other  extraneous  injury. 

The  cable  must  conform  in  quality  and  manufacture  to  a  sample  pre- 
viously approved  by  the  telegraph  company. 

1  Omitting  immersion. 


SPECIFICATIONS  FOR  PAPER  CABLE  455 

SPECIFICATION  FOR  LEAD  COVERED  AERIAL  OR  UNDERGROUND  SATURATED 

PAPER  CABLE 

CONDUCTORS 

Each  conductor  to  be  No.  14  B.  &  S.  gage  (0.064  in.)  soft-drawn  copper 
wire,  in  one  piece  and  free  from  joints. 

INSULATION 

Each  conductor  to  be  insulated  with  three  wrappings  of  the  best  grade 
manila  paper  to  a  diameter  of  158  mils. 

The  whole  core  to  be  served  with  not  less  than  three  thicknesses  of  the 
best  grade  manila  paper  to  a  total  thickness  equal  to  that  on  the  conductors 
and  comprising  not  less  than  two  wrappings.  All  wrappings  to  be  thoroughly 
saturated  with  a  high-grade  insulating  compound. 

LAYERS  AND  MARKING 
The  conductors  to  be  properly  laid  up  with  a  marking  wire  in  each  layer. 

SHEATH 

Sheath  to  be  not  less  than  one-eighth  inch  thick  and  to  contain  3  per 
cent,  of  tin  by  weight,  to  be  uniform  in  composition  and  thickness  and  free 
from  holes,  splices,  joints,  porous  places,  or  other  defects,  and  to  fit  so  closely 
as  to  leave  no  space  between  the  core  and  the  lead. 

ELECTRICAL  TESTS 

The  finished  cable  shall  be  immersed  in  a  tank  of  water  for  24  hours, 
at  the  end  of  which  time  the  dielectric  of  each  conductor  shall  be  subjected 
to  a  strain  of  not  less  than  2,000  volts  alternating  current  applied  for  one 
minute  from  a  suitable  generator  or  transformer.  The  insulation  of  each 
wire  shall  then  be  tested  against  all  other  wires  and  the  sheath  of  the  cable 
and  must  show  a  minimum  insulation  of  200  megohms  per  mile  at  60°  F, 
with  100  volts  applied  for  one  minute.  Each  conductor  of  the  finished  cable 
shall  have  a  resistance  of  not  more  than  14.5  ohms  per  mile  at  a  temperature 
of  68°  F. 

The  above  tests  to  be  made  by  an  authorized  inspector  of  the  telegraph 
company  in  the  presence  of  the  manufacturer's  representative. 

The  Company  requires  the  manufacturer  to  furnish  a  reliable  table  of 
coefficients  of  the  dielectric's  resistance,  showing  its  decrease  above  and 
increase  below  60°  F.,  within  the  limits  of  variations  of  temperature  to  which 


456  AMERICAN  TELEGRAPH  PRACTICE 

the  cable  may  be  subjected  during  tests,  and  the  minimum  of  200  megohms 
per  mile  will  be  modified  accordingly. 

One  conductor  in  each  layer,  as  a  tracer,  to  be  well  tinned,  wrapped  with 
dark  blue  paper  and  wound  spirally  with  medium  weight  black  cotton  thread. 

REELS 

The  finished  cable  to  be  free  from  mechanical  defects  and  to  be  furnished 
in  lengths  as  specified  and  wound  on  reels  of  suitable  diameter.  These  reels 
are  to  have  iron  bushings  of  sufficient  strength  to  safely  carry  the  cable,  and 
the  cable  to  be  wound  thereon  with  both  the  inner  and  outer  ends  so  arranged 
as  to  enable  electrical  tests  to  be  made  of  the  conductors  while  on  the  reel. 
A  tag  shall  be  securely  attached  to  the  reel,  upon  which  shall  be  recorded  the 
manufacturer's  name,  the  exact  number  of  feet  of  cable  upon  the  reel,  the 
number  of  conductors  in  said  cable,  and  the  date  of  shipment  to  the  tele- 
graph company  from  the  factory. 

Immediately  after  the  cable  has  been  tested  and  inspected  by  the  tele- 
graph company's  inspector,  the  ends  of  the  cable  shall  be  sealed  with  solder, 
and  the  inner  end  properly  protected  to  prevent  mechanical  injury  while 
in  transit. 

When  the  manufacturer  is  required  to  draw  the  cable  into  a  subway,  it 
is  to  be  installed  with  the  proper  splices  free  from  all  mechanical  injury. 
Within  thirty  days  after  being  laid,  the  cable  shall  be  tested  as  herin  described 
by  an  authorized  inspector  of  the  telegraph  company  and  must  show  the 
insulation  herein  required. 

If  the  diameter  of  the  cable  called  for  in  this  specification  is  too  great  to 
admit  of  its  being  pulled  into  the  duct  of  the  subway  provided,  the  Company 
is  to  be  notified  prior  to  the  manufacture  of  the  cable. 

MANUFACTURER'S  GUARANTEE 

The  manufacturer  to  guarantee  the  perfection  of  the  cable  and  that  the 
cable  will  remain  in  good  working  condition  during  a  telegraph  or  telephone 
service  of  one  year  after  it  is  delivered.  During  the  first  year  after  the  cable 
is  purchased  the  manufacturer  to  repair  any  defects  due  to  faulty  materials 
or  manufacture,  or  to  reimburse  the  company  for  expenditures  incurred  in 
repairing  such  defects.  The  manufacturer  not  to  be  responsible  for  defects 
caused  by  mechanical  injury. 

SPECIFICATION  FOR    LEAD -COVERED    TWISTED-PAIR  PAPER   SUBMARINE 

CABLE 

CONDUCTORS 

Conductors  to  be  of  gage  as  ordered,  of  soft-drawn  copper  wire,  prefer- 
ably in  one  piece,  free  from  joints;  when  joints  are  made  they  must  be"  so 
brazed  that  there  will  be  no  reduction  in  the  tensile  strength  of  the  wire. 


SPECIFICATIONS  FOR  SUBMARINE  CABLE  457 

INSULATION 

Each  conductor  shall  be  insulated  with  not  less  than  three  spiral  wrappings 
of  the  best  grade  manila  paper,  so  that  the  total  thickness  of  the  insulating 
wall  will  be  between  46  and  48  mils. 

TWISTS  OF  PAIRS  AND  MARKING 

The  two  wires  of  a  pair  shall  be  twisted  together,  the  length  of  the  lay 
not  to  exceed  6  in.  The  conductors  of  each  pair  to  be — one  red  and  one 
white,  and  one  white  conductor  in  each  layer  to  be  spirally  wound  with  coarse 
black  thread  for  a  layer  tracer. 

CORE 

The  twisted  pairs  shall  be  laid  up  into  a  cylindrical  core  with  the  layers 
in  reverse  directions.  The  whole  core  to  be  served  with  not  less  than  three 
thicknesses  of  the  best  grade  manila  paper  to  a  total  wall  thickness  equal  to 
that  on  the  conductors  and  comprising  not  less  than  two  wrappings. 

The  cable  must  be  laid  up  very  compactly.  For  this  reason  the  paper 
insulation  should  be  applied  loosely  so  that  when  the  pairs  are  tightly  cabled 
together,  the  interstices  between  the  conductors  shall  be  filled  with  dense 
paper.  In  the  event  of  the  number  of  pairs  called  for  not  permitting  the 
construction  of  a  compact  core,  the  number  of  pairs  may  be  exceeded  by  the 
amount  necessary  to  insure  such  construction. 

SHEATH 

The  lead  covering  must  be  of  uniform  composition  and  thickness,  con- 
taining 3  per  cent,  of  tin  by  weight,  and  free  from  holes,  splices,  joints, 
porous  places  or  other  defects;  and  shall  fit  so  tightly  as  to  make  the  core 
compact. 

The  thickness  shall  be  in  accordance  with  the  following  sizes  of  armor  wire : 

For  No.  4  B.  W.  G.,  sheath  to  be  3/16  in.  thick. 
For  No.  6  B.  W.  G.,  sheath  to  be  1/8  in.  thick. 
For  No.  8  B.  W.  G.,  sheath  to  be  1/8  in.  thick. 

JUTE  COVERING  OVER  SHEATH 

The  lead  sheath  shall  be  covered  with  three  layers  of  jute,  tightly  and 
spirally  wound  in  reverse  directions,  to  a  total  wall  thickness  of  3/16  of  an 
inch,  thoroughly  saturated  with  a  compound  which  shall  be  impervious  to 
water  and  resist  .electrolytic  action  between  the  lead  sheath  and  the  zinc 
coating  of  the  armor. 


458 


AMERICAN  TELEGRAPH  PRACTICE 
ARMOR 


Outside  of  the  jute  specified  above,  an  armor  of  Ex.  B.  B.  galvanized  iron 
wire,  gage  as  ordered,  shall  be  laid  on  without  twisting,  with  a  lay  of  ten  times 
the  diameter  of  the  cable  over  the  armor. 


GALVANIZING  OF  ARMOR  WIRES 

The  galvanized  wire  used  for  the  armor  must  comply  with  the  specifica- 
tions of  the  telegraph  company  for  galvanized  iron  wire. 

JUTE  SERVING  OVER  ARMOR 

Outside  of  the  armor  shall  be  placed  two  wraps  of  jute  laid  on  in  reverse 
directions  and  thoroughly  saturated  with  a  preservative  compound  consisting 
of  65  parts  of  mineral  pitch,  30  parts  of  fine  sand  and  5  parts  of  tar. 

The  completed  cable  shall  have  a  coating  of  soapstone  to  prevent  the  turns 
from  sticking  to  each  other  on  the  reel. 

ELECTRICAL  TESTS 

After  the  sheath  has  been  put  on,  but  before  it  is  served  with  jute  and 
armored,  the  cable  shall  be  immersed  in  a  tank  of  water  for  24  hours,  at  the 
end  of  which  time  the  dielectric  of  each  conductor  shall  be  subjected  to  a 
strain  of  not  less  than  1,000  volts  alternating-current  applied  for  one  minute 
from  a  suitable  generator  or  transformer.  Each  wire  shall  then  be  tested 
for  insulation  against  all  other  wires  and  the  sheath  of  the  cable,  and  must 
show  a  minimum  of  1,000  megohms  per  mile  at  60°  F.  with  100  volts  applied 
for  one  minute. 

Each  conductor  shall  have  a  resistance  and  an  electrostatic  capacity 
which  shall  not  exceed  those  specified  in  the  following  table: 


Gage  B.  &  S. 

Resistance  per  mile  in 
ohms  at  68°  F.  of 
any  wire 

Mutual  capacity  per 
mile  in  m'f'ds  of 
any  pair 

Average  mutual 
capacity  per 
mile  in  m'f'ds  of 
all  pairs 

12 
13 

9.1 
"•5 

0.150 
0.125 

O.  121 
0.108 

14 

14-5 

o.  100 

O.OQ5 

The  finished  cable  on  the  shipping  reel  shall  again  be  immersed  and  tested 
as  above,  and  meet  the  same  requirements. 

The  above  tests  to  be  made  by  a  regularly  authorized  inspector  of  the 
telegraph  company  in  the  presence  of  the  manufacturer's  representative. 


SPECIFICATIONS  FOR  TWISTED-PAIR  CABLE  459 

FILLING  OF  ENDS 

The  ends  of  each  length  of  cable  must  be  filled  with  an  insulating  material 
which  will  seal  the  cable  for  a  distance  of  2  ft.  or  more  from  each  end. 

REELS 

The  finished  cable  to  be  free  from  all  kinds  of  mechanical  defects  and  to 
be  furnished  in  lengths  as  specified,  and  wound  on  reels  of  suitable  diameter. 
These  reels  are  to  have  iron  bushings  of  sufficient  strength  to  safely  carry  the 
cable  which  is  to  be  wound  thereon  with  both  the  inner  and  the  outer  ends 
so  arranged  that  electrical  tests  of  the  conductors  can  be  made  while  on  the 
reel. 

A  tag  shall  be  securely  attached  to  the  reel,  upon  which  shall  be  recorded 
the  manufacturer's  name,  the  exact  number  of  feet  of  cable  upon  the  reel, 
the  number  of  conductors  in  the  cable,  the  reel  number,  and  the  date  of  ship- 
ment to  the  telegraph  company  from  the  factory. 

Immediately  after  the  cable  has  been  tested  and  inspected  by  the  tele- 
graph company's  inspector,  the  ends  of  the  cable  shall  be  sealed  with  solder, 
and  the  inner  end  properly  protected  to  prevent  mechanical  injury  while  in 
transit. 

MANUFACTURER'S  GUARANTEE 

The  manufacturer  to  guarantee  the  perfection  of  the  cable  and  that  the 
cable  will  remain  in  good  working  condition  during  a  telegraph  or  telephone 
service  of  one  year  after  it  is  delivered.  During  the  first  year  after  the  cable 
is  purchased,  the  manufacturer  to  repair  any  defects  due  to  faulty  material 
or  manufacture,  or  to  reimburse  the  telegraph  company  for  expenditures 
incurred  in  repairing  such  defects.  The  manufacturer  not  to  be  responsible 
for  defects  caused  by  mechanical  injury. 

SPECIFICATION  FOR  LEAD-COVERED  TWISTED-PAIR  PAPER  CABLE 

CONDUCTORS 

Conductors  to  be  of  gage  as  ordered,  of  soft-drawn  copper  wire,  prefer- 
ably in  one  piece,  free  from  joints;  when  joints  are  made  they  must  be  so 
brazed  that  there  will  be  no  reduction  in  the  tensile  strength  of  the  wire. 

INSULATION 

Each  conductor  shall  be  insulated  with  not  less  than  three  spiral  wrap- 
pings, with  a  half -width  lap,  of  the  best  grade  manila  paper,  so  that  the  total 
thickness  of  the  insulating  wall  will  be  between  46  and  48  mils. 


460  AMERICAN  TELEGRAPH  PRACTICE 

TWISTS  OF  PAIRS  AND  MARKING 

The  two  wires  of  a  pair  shall  be  twisted  together,  the  length  of  the  lay 
not  to  exceed  6  in.  The  conductors  of  each  pair  to  be — one  red  and  one  white, 
except  those  of  the  tracer  pair  in  each  layer,  which  are  to  be — one  white  and 
one  dark  blue,  the  latter  spirally  wound  with  coarse  white  thread. 

CORE 

The  twisted  pairs  shall  be  laid  up  into  a  cylindrical  core  with  the  layers 
in  reverse  directions.  The  whole  core  to  be  served  with  not  less  than  three 
thicknesses  of  the  best  grade  manila  paper  to  a  total  wall  thickness  equal  to 
that  on  the  conductors  and  comprising  not  less  than  two  wrappings  with  a 
half-width  lap. 

The  cable  must  be  laid  up  very  compactly.  For  this  reason  the  paper 
insulation  should  not  be  applied  too  tightly,  so  that  when  the  pairs  are  tightly 
cabled  together,  the  interstices  between  the  conductors  shall  be  filled  with 
dense  paper.  In  the  event  of  the  number  of  pairs  called  for  not  permitting 
the  construction  of  a  compact  core,  the  number  of  pairs  may  be  exceeded 
by  the  amount  necessary  to  insure  such  construction. 

SHEATH 

The  lead  covering  must  be  of  uniform  composition  and  thickness,  contain 
3  per  cent,  of  tin  by  weight,  and  be  free  from  holes,  splices,  joints,  porous 
places  or  other  defects.  It  shall  be  not  less  than  i/8-in.  thick  and  shall  fit 
so  tightly  as  to  make  the  core  compact. 

OVER-ALL  DIAMETER 

The  manufacturers  must  ascertain  the  permissible  over-all  diameter  of 
the  finished  cable  when  order  is  placed. 

FILLING  OF  ENDS 

The  ends  of  each  length  of  cable  must  be  filled  with  an  insulating  material 
which  will  seal  the  cable  for  a  distance  of  2  ft.  or  more  from  each  end. 

ELECTRICAL  TESTS 

The  finished  cable  shall  be  immersed  in  a  tank  of  water  for  24  hours,  at 
the  end  of  which  time  the  dielectric  of  each  conductor  shall  be  subjected  to 
a  strain  of  not  less  than  i  ,000  volts  alternating  current  applied  for  one  minute 


SPECIFICATIONS  FOR  TWISTED-PAIR  CABLE 


461 


from  a  suitable  generator  or  transformer.  Each  wire  shall  then  be  tested 
for  insulation  against  all  other  wires  and  the  sheath  of  the  cable,  and  must 
show  a  minimum  of  1,000  megohms  per  mile  ar  60°  F.  with  100  volts  applied 
for  one  minute. 

Each  conductor  shall  have  a  resistance  and  an  electrostatic  capacity 
which  shall  not  exceed  those  specified  in  the  following  table : 


Resistance  per  mile 
in  ohms  at  68°  F.  of 


Mutual  capacity  per        Average  mutual 
mile  in  m'f'ds  of 


any  wire 

any  pair 

m'f'ds  of  all  pairs 

12 

9.1 

o.  150 

O  .  I  2  I 

13 

n-5 

o.  125 

o.  108 

14 

14-5 

O.  TOO 

0.095 

16 

23-5 

0.092 

0.087 

REELS 

The  finished  cable  to  be  free  from  all  kinds  of  mechanical  defects  and  to 
be  furnished  in  lengths  as  specified,  and  wound  on  reels  of  suitable  diameter. 
These  reels  are  to  have  iron  bushings  of  sufficient  strength  to  safely  carry  the 
cable  which  is  to  be  wound  thereon  with  both  the  inner  and  the  outer  ends 
so  arranged  that  electrical  tests  of  the  conductors  can  be  made  while  on  the 
reel. 

A  tag  shall  be  securely  attached  to  the  reel,  upon  which  shall  be  recorded 
the  manufacturer's  name,  the  exact  number  of  feet  *of  cable  upon  the  reel, 
the  number  of  conductors  in  the  cable,  the  reel  number,  and  the  date  of 
shipment  to  the  company  from  the  factory. 

Immediately  after  the  cable  has  been  tested  and  inspected  by  the  tele- 
graph company's  inspector,  the  ends  of  the  cable  shall  be  sealed  with  solder, 
and  the  inner  end  properly  protected  to  prevent  mechanical  injury  while  in 
transit. 


MANUFACTURER'S  GUARANTEE 

The  manufacturer  to  guarantee  the  perfection  of  the  cable  and  that  the 
cable  will  remain  in  good  working  condition  during  a  telegraph  or  telephone 
service  of  one  year  after  it  is  delivered.  During  the  first  year  after  the  cable 
is  purchased,  the  manufacturer  to  repair  any  defects  due  to  faulty  material 
or  manufacture,  or  to  reimburse  the  company  for  expenditures  incurred  in 
repairing  such  defects.  The  manufacturer  not  to  be  responsible  for  defects 
caused  by  mechanical  injury. 


462  AMERICAN  TELEGRAPH  PRACTICE 

SPECIFICATION  FOR  AERIAL   (RUBBER  COMPOUND  DIELECTRIC)    CABLE 

All  conductors  to  be  of  No.  14  B.  &  S.  (64  mils  diameter)  thoroughly 
annealed  copper,  98  per  cent,  pure,  according  to  Matthiessen's  standard, 
equal  in  strength,  finish,  and  pliability  to  the  best  market  grade,  well  tinned 
and  uniformly  coated  to  a  diameter  of  158  mils  with  a  high-grade  rubber 
permanent  insulating  compound,  which  shall  adhere  closely  to  the  wire, 
and  which  shall  not  deteriorate  under  ordinary  conditions. 

Each  insulated  conductor,  before  being  laid  up  into  cable  form,  must 
have  its  dielectric  subjected  in  water,  after  24  hours  immersion,  to  a  strain 
of  not  less  than  i  ,000  volts  alternating  current  between  the  conductor  and  the 
water,  applied  for  one  minute  from  a  suitable  generator  or  transformer; 
and  must  show  while  in  the  tank,  after  such  immersion,  an  insulation  of  not 
less  than  300  megohms  per  mile  at  60°  F.,  with  not  less  than  100  volts  applied 
for  one  minute.  Test  to  be  made  by  standard  testing  instruments  in  the 
presence  of  an  inspector  of  the  telegraph  company. 

All  conductors  for  test,  either  in  coils  or  reels,  must  have  tags  securely 
attached,  giving  in  plain  figures  the  coil  or  reel  numbers,  the  number  of  feet 
in  each  coil  or  reel,  the  gage  of  wire,  and  diameter  of  insulation;  and  such 
coils  must  so  far  as  practicable  be  in  uniform  lengths  corresponding  to  the 
length  of  the  cable. 

One  of  the  conductors  in  each  layer  of  the  cable  must  be  suitably  corded 
for  tracing. 

Each  insulated  conductor  in  the  cable  must  be  protected  by  a  closely 
woven  cotton  braid  of  not  less  than  15  mils  thickness,  thoroughly  saturated 
with  a  compound  which  is  not  soluble  in  water,  which  does  not  act  injuriously 
upon  the  permanent  insulating  compound,  braid  or  tape,  and  which  is  not 
objectionable  to  handle. 

In  case  the  number  of  conductors  do  not  permit  of  layers  in  the  mathe- 
matical ratio  of  i,  7,  19,  37,  61,  91,  etc.,  small  strands  of  semi-saturated  jute 
are  to  be  used  to  render  the  lay-up  of  the  cable  symmetrical  and  also  to 
protect  the  insulation  of  the  conductors  when  the  cable  is  subjected  to  bends 
and  twists. 

The  cable  must  be  wrapped  over  all  with  flexible  cotton  tape  of  first-class 
quality,  saturated  with  first-class  weatherproof  compound.  The  tape  must 
not  be  less  than  20  mils  thick,  must  have  a  lap  of  one-half  its  width,  and 
firm  adherence  where  lapped,  so  that  it  will  not  readily  come  apart.  Over 
this  the  cable  must  have  a  durable  protection  of  circular  loom,  braid,  or 
tape  covering,  acceptable  to  the  telegraph  company,  thoroughly  saturated 
with  the  aforesaid  compound. 

The  finished  cable  must  not  be  sticky  or  objectionable  to  handle. 

All  cable  made  up  as  above,  prior  to  shipment  from  factory,  and  after 
being  placed  upon  reels,  must  have  each  length  again  tested  for  insulation 
by  the  inspector  of  the  telegraph  company. 


SPECIFICATIONS  FOR  OFFICE  CABLE  463 

Each  conductor  under  test  must  show  an  insulation  (when  all  of  the 
other  conductors  of  the  length  are  grounded)  of  not  less  than  500  megohms 
per  mile  at  60°  F.,  with  not  less  than  100  volts  applied  for  one  minute.  This 
test  to  be  made  without  immersion. 

The  conductors  of  the  completed  cable  must  also  be  tested  for  continuity, 
and  the  inspector  shall  make  such  tests  for  capacity  and  conductivity  as  he 
thinks  advisable. 

The  contractor  will  be  required  to  furnish  a  table  of  coefficients  of  the 
resistance  of  the  dielectric,  showing  its  decrease  above  and  its  increase  below 
60°  F.,  within  the  limits  of  variation  of  temperature  to  which  the  cable  may 
be  subjected 'during  test. 

The  reels  upon  which  the  cable  is  shipped  must  be  strong  and  well  pro- 
tected, and  the  cable  neatly  wound  thereon  with  both  ends  so  arranged 
that  tests  of  the  conductors  on  the  reels  may  readily  be  made. 

A  tag  must  be  securely  fastened  to  each  reel,  upon  which  the  contractor 
must  record  the  exact  number  of  feet  from  end  to  end  of  the  cable  upon  the 
reel,  the  number  of  conductors  in  the  cable,  and  the  date  of  shipment  to 
the  company  from  the  contractor's  factory. 

'The  contractor  must  give  the  usual  guarantee  that  the  cable  will  remain 
in  good  condition  for  one  year  after  delivery,  provided  it  is  not  used  for 
currents  of  over  i  ampere,  or  having  an  electromotive  force  of  over  500 
volts;  and  must  agree  to  repair  or  to  reimburse  the  telegraph  company  for 
any  expenditures  incurred  in  repairing  defects  that  may  appear  during  that 
period,  not  caused  by  mechanical  or  other  extraneous  injury. 

The  cable  must  conform  in  quality  and  manufacture  to  a  sample  pre- 
viously approved  by  the  telegraph  company. 

SPECIFICATION  FOR  OFFICE  CABLE 

All  conductors  to  be  of  No.  19  B.  &  S.  (36  mils  diameter)  thoroughly 
annealed  copper,  98  per  cent,  pure,  according  to  Matthiessen's  standard, 
equal  in  strength,  finish,  and  pliability  to  the  best  market  grade,  well  tinned 
and  uniformly  coated  to  a  diameter  of  101  mils  with  a  high-grade  permanent 
insulating  compound,  which  shall  adhere  closely  to  the  wire,  and  which  shall 
not  deteriorate  under  ordinary  conditions. 

Each  insulated  conductor,  before  being  laid  up  into  cable  form,  must  have 
its  dielectric  subjected  in  water,  after  24  hours  immersion,  to  a  strain  of  not 
less  than  1,000  volts  alternating  current  between  the  conductor  and  the  water, 
applied  for  one  minute  from  a  suitable  generator  or  transformer;  and  must 
show  while  in  the  tank,  after  such  immersion,  an  insulation  of  not  less  than 
300  megohms  per  mile  at  60°  F.,  with  not  less  than  100  volts  applied  for 
one  minute.  Test  to  be  made  by  standard  testing  instruments  in  the  presence 
of  an  inspector  of  the  telegraph  company. 


464  AMERICAN  TELEGRAPH  PRACTICE 

All  conductors  for  test,  either  in  coils  or  reels,  must  have  tags  securely 
attached,  giving  in  plain  figures  the  coil  or  reel  numbers,  the  number  of  feet 
in  each  coil  or  reel,  the  gage  of  wire,  and  diameter  of  insulation;  and  such 
coils  must  so  far  as  practicable  be  in  uniform  lengths  corresponding  to  the 
length  of  the  cable. 

One  of  the  conductors  in  each  layer  of  the  cable  must  be  suitably  corded 
for  tracing. 

Each  insulated  conductor  in  the  cable  must  be  protected  by  a  closely 
woven  cotton  braid  of  not  less  than  1 5  mils  thickness,  thoroughly  saturated 
with  a  compound  which  is  not  soluble  in  water,  which  does  not  act  injuriously 
upon  the  permanent  insulating  compound,  braid  or  tape,  and  which  is  not 
objectionable  to  handle. 

The  conductors  must  be  so  laid  up  as  to  make  the  completed  cable 
sufficiently  flexible  to  permit  it  to  be  bent  without  buckling  to  the  diameter 
given  in  the  following  table. 

Diameters  of  drums  on  which  office  cables  must  bend  without  buckling: 

5  conductor 2  in. 

10  conductor 5  in. 

25  conductor 9  in. 

50  conductor 14  in. 

The  cable  must  be  wrapped  over  all  with  flexible  cotton  tape  of  first-class 
quality,  saturated  with  first-class  weatherproof  compound.  The  tape  must 
not  be  less  than  20  mils  thick,  must  have  a  lap  of  one-half  its  width,  and  firm 
adherence  where  lapped,  so  that  it  will  not  readily  come  apart. 

The  finished  cable  must  not  be  sticky  or  objectionable  to  handle. 

All  cable  made  up  as  above,  prior  to  shipment  from  factory,  and  after 
being  placed  upon  reels,  must  have  each  length  again  tested  for  insulation 
by  the  inspector  of  the  telegraph  company;  and  each  conductor  under  test 
must  show  an  insulation  (when  all  of  the  other  conductors  of  the  length  are 
grounded)  of  not  less  than  500  megohms  per  mile  at  60°  F.,  with  not  less  than 
100  volts  applied  for  i  minute  in  the  usual  manner.1  The  conductors  of  the 
completed  cable  must  also  be  tested  for  continuity,  and  the  inspector  shall 
make  such  tests  for  capacity  and  conductivity  as  he  thinks  advisable. 

The  contractor  will  be  required  to  furnish  a  table  of  coefficients  of  the 
resistance  of  the  dielectric,  showing  its  decrease  above  and  its  increase 
below  60°  F.,  within  the  limits  of  variation  of  temperature  to  which  the  cable 
may  be  subjected  during  test. 

The  reels  upon  which  the  cable  is  shipped  must  be  strong  and  well  pro- 
tected, and  the  cable  neatly  wound  thereon  with  both  ends  so  arranged  that 
tests  of  the  conductors  on  the  reels  may  readily  be  made. 

A  tag  must  be  securely  fastened  to  each  reel  upon  which  the  contractor 
must  record  the  exact  number  of  feet  from  end  to  end  of  the  cable  upon  the 

1  Omitting  immersion. 


SPECIFICATIONS  FOR  OFFICE  WIRES  465 

reel,  the  number  of  conductors  in  the  cable,  and  the  date  of  shipment  to 
the  telegraph  company  from  the  contractor's  factory. 

The  contractor  must  give  the  usual  guarantee  that  the  cable  will  remain 
in  good  condition  for  one  year  after  delivery,  provided  it  is  not  used  for  cur- 
rents of  over  i  ampere,  or  having  an  electromotive  force  of  over  500  volts; 
and  must  agree  to  repair  or  to  reimburse  the  telegraph  company  for  any  ex- 
penditures incurred  in  repairing  defects  that  may  appear  during  that  period, 
not  caused  by  mechanical  or  other  extraneous  injury. 

The  cable  must  conform  in  quality  and  manufacture  to  a  sample  previ- 
ously approved  by  the  telegraph  company. 

SPECIFICATION  FOR  OFFICE  WIRES 

CONDUCTORS 

Conductors  to  be  of  gage  as  ordered,  of  soft-drawn  copper  wire  not  less 
than  98  per  cent,  pure,  preferably  in  one  piece  free  from  joints.  When 
joints  are  made,  they  must  be  so  brazed  that  there  will  be  no  reduction  in  the 
tensile  strength  or  conductivity  of  the  wire. 

Wire  must  be  tinned  and  uniformly  coated  with  high-grade  insulating 
compound  to  the  thickness  specified. 


BRAID 

Colored  braid,  when  required,  must  be  of  the  specified  thickness,  closely 
woven  and  with  smooth  surface.  It  is  to  be  made  of  good  quality  strong 
cotton  thread  fast  colored  with  non-injurious  dyes. 

Braid  on  office  wire  must  be  made  of  closely  woven,  fire-proofed,  strong 
cotton  thread. 

Saturated  braid  must  be  filled  with  a  first-class,  water-proof,  insulating 
compound  which  will  give  a  smooth  surface,  but  which  will  not  be  injurious 
to  braid  or  rubber,  become  tacky  at  the  highest  summer  or  crack  at  the 
lowest  winter  temperatures. 

Each  wire  of  twisted  pairs  must  be  braided  separately  and  one  of  the  wires 
suitably  marked  for  tracing. 

ELECTRICAL  TESTS 

The  wire  after  being  braided  (except  in  the  case  of  office  wire)  shall  be 
immersed  in  a  tank  of  water  for  24  hours  at  the  end  of  which  time  its  dielectric 
shall  be  subjected  to  a  strain  of  not  less  than  500  volts  alternating  current  for 
two  seconds  for  5o-megohm  wires,  and  1,000  volts  alternating  current  for 
five  seconds  for  the  500-  and  the  75o-megohm  wires. 

30 


466 


AMERICAN  TELEGRAPH  PRACTICE 


The  insulation  of  each  length  shall  be  tested  in  the  usual  manner  with  100 
volts  applied  for  one  minute  at  60°  F. 

Office  wire  must  be  immersed  and  tested  as  above  before  the  braid  is  put  on. 
After  braiding,  samples  must  be  submitted  for  approval. 


COILS 

Coils  under  test  must  be  serially  numbered  and  so  far  as  practicable  in 
uniform  lengths  of  500,  1,000  or  2,000  ft.  Subsequently  the  wire  must  be  cut 
into  lengths  to  conform  with  the  order. 

Each  accepted  coil  must  be  neatly  laid  up  and  wrapped  in  paper  or  burlap. 
After  wrapping,  a  tag  giving  length,  weight,  gage,  kind,  color,  and  manu- 
facturer's name  must  be  securely  fastened  to  the  inside  of  each  coil. 

The  coils  wrapped  and  tagged  as  above  must  be  packed  in  barrels  which 
are  to  be  plainly  marked,  showing  the  size  or  gage,  kind,  color  and  total 
number  of  feet  in  each  barrel. 

TABLE  OF  STANDARD  RUBBER  COMPOUND  INSULATED  WIRES 


Conductor 

Minimum 
diameter 

Braid 

Minimum 
megohms 

Name 

B.  &S. 
gage 

wire  with- 
out braid 
mils1 

Thickness 
mils 

Color  and  finish 

per  mile 
60°  F. 
100  volts 

Office 

16 

113 

i  3 

Gray  flame  proof 

COO 

Bridle  

14 

158 

20 

Black  saturated 

750 

Pothead  and  battery 
stems. 

14 

140 

No  braid 

750 

Call  circuit  

16 

II3 

20 

Black  saturated 

CO 

Outside  twisted  pair. 

14 

158 

20 

Black  saturated 

750 

Annunciator  

18 

IO2 

IIT 

Glazed    cotton 

CO 

color  as  ordered. 

Annunciator  twisted 
pair. 

18 

IO2 

15 

Glazed    cotton, 
color  as  ordered. 

50 

1  Maximium  allowable  diameter  of  insulated  wire  without  braid  5  mils  above  minimum. 


CHAPTER  XXIV 
ELECTROLYSIS  OF  UNDERGROUND  CABLE  SHEATHS 

When  two  pieces  of  metal  are  immersed  in  an  electrolyte  consisting  of 
slightly  acidulated  water,  and  a  current  of  electricity  is  passed  between  tjiem, 
minute  particles  of  one  of  the  metals  are  decomposed  and  deposited  upon 
the  surface  of  the  other  metal.  The  action  is  the  same  as  that  which  takes 
place  in  the  process  of  electroplating.  The  detached  particles  are  carried 
from  one  metal  to  the  other  in  the  same  direction  the  current  travels — from 
positive  to  negative  plate. 

A  similar  action  takes  place  between  the  sheaths  of  buried  cables  and  the 
tracks  of  electric  railroad  systems.  The  positive  pole  of  the  railroad  power 
dynamo  is  connected  to  the  feeder  system  and  the  negative  pole  of  the 
dynamo  to  the  steel  rails,  making  a  circuit  via  the  car  trolley  or  shoe  equip- 
ment through  the  car  motors  and  back  to  the  generating  station  over  the 
track. 

Where  the  rails  are  in  contact  with  the  earth  either  directly  or  indirectly 
(by  way  of  metal  supporting  structures)  the  current  in  the  rails  has  a  tend- 
ency to  leak  away  from  the  track  and  travel  back  to,  or  in  the  direction  of,  the 
power  station.  Obviously,  wherever  metal  pipe  systems  are  buried  in  the 
earth  adjacent  to  electric  railroad  tracks,  the  former  in  many  cases  will  form 
a  branch  of  a  joint-circuit  constituting  the  return  path  of  the  railroad  current. 
If  the  rails  were  perfectly  insulated  from  the  earth  or  were  laid  in  perfectly 
dry  ground  this  action  could  not  take  place,  but  in 'most  localities  there  is  a 
sufficient  amount  of  moisture  beneath  the  surface  of  the  earth  to  act  as  an 
electrolyte.  The  earth  serves  the  purpose  of  an  electroplating  tank,  as  it 
has  all  the  elements  required,  namely,  the  car  tracks  and  cable  sheaths  sepa- 
rated by  a  more  or  less  moisture-saturated  compound. 

The  fact  that  the  sheaths  of  the  buried  cables  act  as  conductors  for  a 
portion  of  the  return  current  is  not  of  much  concern,  but  if  while  serving  as  a 
conductor  the  sheath  is  immersed  in  an  electrolyte,  the  danger  is  that  a  por- 
tion of  the  current  will  leave  the  conductor  and  pass  through  the  electrolyte 
to  another  conductor,  for  in  that  case  it  will  carry  particles  of  the  sheath  to 
the  surface  of  the  second  conductor,  and  while  this  action  does  not  particu- 
larly menace  the  usefulness  of  the  latter  it  soon  results  in  disintegration  of  the 
cable  sheath  with  the  result  that  moisture  is  permitted  to  enter  the  cable 
causing  leaks,  crosses,  short  circuits  and  grounding  of  the  conductors  con- 
tained in  the  cable. 

467 


468  AMERICAN  TELEGRAPH  PRACTICE 

The  amount  of  current  which  escapes  from  a  track  to  adjacent  pipe  lines 
depends  upon  the  relative  electrical  distance  of  the  track  circuit,  the  earth  and 
the  pipe  line,  with  regard  to  the  location  of  the  power  house.  A  very  small 
current  volume,  however,  will  produce  electrolytic  action.  For  example,  one 
ampere  flowing  one  hour  dissolves  0.035  oz-  °f  cast  iron,  0.105  oz-  °f  wrought 
iron,  and  0.125  oz.  of  lead.  In  practice,  of  course,  the  current  does  not  often 
flow  from  any  one  point,  but  is  spread  out  over  a  considerable  length  of  cable 
or  track;  but  it  will  be  realized  that  even  where  the  surfaces  affected  have 
considerable  area,  where  the  action  continues  for  any  great  length  of  time  the 
result  will  be  disastrous.  The  ideal  remedy  is  to  provide  a  return  circuit  for 
the  railway  current  of  sufficient  capacity  to  reduce  leakage  to  the  lowest 
possible  degree,  by  properly  bonding  the  rails  or  by  installing  an  auxiliary 
return  wire  of  large  section  bonded  to  the  rails  at  intervals,  but  even  where 
this  is  done,  at  points  remote  from  the  power  house  neighboring  pipe  systems 
are  still  likely  to  form  branches  of  a  joint-circuit  back  to  the  negative  terminal 
of  the  dynamo. 

Where  the  current  passes  from  the  tracks  to  the  cable  sheath  or  to  a  pipe 
line,  no  damage  will  be  done  to  either  of  the  latter,  but  the  tracks  themselves 
will  be  eaten  away.  Where  the  current  leaves  the  sheath  or  pipe,  however, 
and  passes  to  the  tracks  or  to  other  pipe  systems,  damage  will  be  done  to  the 
sheath  or  pipe  at  the  point  or  points  where  the  current  leaves  them. 

When  any  interruption  occurs  to  the  track  return  circuit,  as,  for  instance, 
when  a  bond  is  broken,  or  a  rail  is  broken  or  temporarily  removed,  a  large 
proportion  of  the  return  current  is  shunted  around  the  break  through  ad- 
jacent pipe  lines  and  the  large  current  volume  diverted  through  the  latter 
within  a  very  short  time  causes  serious  damage  at  the  point  where  the  current 
leaves  the  sheath  or  pipe  in  returning  to  the  track  rails  at  a  point  on  the  gen- 
erator side  of  the  interruption. 

In  order  to  determine  where  electrolysis  is  liable  to  occur,  it  is  well  to 
obtain  or  prepare  a  map  showing  the  location  of  manholes  and  cables  and 
the  routes  they  take.  Upon  this  map  the  electric  railway  lines  may  be 
traced  with  red  ink.  At  all  manholes  measurements  should  be  made  between 
the  rails  and  cables,  water-pipes,  gas-pipes,  manhole  frame  (if  metal),  water 
in  manhole,  other  cables  and  in  fact  all  metal  objects  that  are  buried  in  the 
ground  in  that  neighborhood  which  would  in  any  way  affect  the  cables. 

In  making  the  measurements  a  voltmeter  with  a  low  reading  scale  should 
be  used,  attaching  a  wire  to  the  positive  terminal  of  the  meter  and  another 
wire  to  the  negative  terminal.  The  free  ends  of  the  wires  should  be  attached 
to  strips  of  lead  or  to  steel  rods  (old  steel  files  with  sharp  points  make  good 
substitites)  as  it  is  found  that  when  the  ends  of  the  copper  wires  are  used  a 
local  action  sometimes  takes  place  which  interferes  with  the  true  readings. 

If,  when  the  wire  attached  to  the  positive  terminal  of  the  voltmeter  is 
placed  in  contact  with  the  rail,  water-pipe,  water  in  the  manhole,  manhole 


ELECTROLYSIS  OF  UNDERGROUND  CABLE  SHEATHS    469 

frame,  or  other  object,  while  the  wire  attached  to  the  negative  terminal  of  the 
voltmeter  is  placed  in  contact  with  the  cable  sheath;  the  voltmeter  pointer 
is  deflected  to  the  right,  the  indication  means  that  a  current  is  flowing  from 
the  rail,  pipe  or  manhole  frame,  etc.,  to  the  cable  sheath.  If  the  deflection  is 
in  the  same  direction  as  contact  is  made  with  each  object,  a  record  should  be 
made  to  the  effect  that  the  cable  is  —  (negative)  to  the  earth  at  that  point,  the 
rail,  and  to  other  pipe  systems.  If  it  is  found  when  contact  is  made  in  any 
instance  that  the  pointer  deflects  to  the  left  the  indication  means  that  cur- 
rent is  flowing  from  the  cable  sheath  to  the  neighboring  object  and  that  the 
sheath  is  being  slowly  eaten  away.  The  exact  difference  of  potential  may  be 
learned  by  reversing  the  wires  in  the  binding-posts  of  the  voltmeter  so  that 
the  pointer  may  move  from  its  zero  position  at  the  extreme  left  of  the  scale,  to 
a  point  on  the  right  which  indicates  the  existing  voltage. 

If  a  reliable  low-reading  voltmeter  is  not  at  hand,  and  a  Weston  galvanom- 
eter is  available,  the  latter  may  be  used  for  electrolysis  tests  by  connecting 
an  external  resistance  of  5,000  ohms  in  series  with  the  galvanometer.  Then, 
with  no  shunt  around  the  galvanometer  movement  coil,  the  scale  will  have 
a  reading  of  o.i  volt,  in  o.oi-volt  divisions.  Using  the  one- tenth  shunt,  the 
scale-reading  will  have  a  value  of  i  volt  in  divisions  of  o.i  volt.  Using  the 
one  one-hundredth  shunt  the  scale  will  have  a  value  of  10  volts  in  divisions 
of  i  volt. 

CABLE  TO  CABLE,  AND  CABLE  TO  RAIL  BONDING 

Undoubtedly  there  are  instances  of  electrolytic  corrosion  of  cable  sheaths 
not  attributable  to  stray  railway  currents,  such,  for  instance,  as  occur  where 
cables  are  laid  in  earth  strewn  with  cinders,  or  where  the  character  of  the  soil 
in  which  the  cable  is  buried  is  such  that  galvanic  action  takes  place  between 
the  cable  sheath  and  neighboring  metallic  substances,  or  in  cases  where  dur- 
ing the  winter  months  frozen  water-pipes  are  thawed  out  by  heating  them  by 
passing  currents  of  large  volume  through  the  frozen  sections  for  a  number  of 
hours,1  but  inasmuch  as  the  bulk  of  the  trouble  experienced  is  due  to  electric- 
railway  return  currents,  it  is  good  practice  to  take  all  possible  precautions 
to  insure  a  low  resistance  return  path  to  the  power  station  for  these  currents. 

In  some  instances  it  has  been  found  advisable  to  run  bare  stranded  copper- 
wire  cables  parallel  to  and  bonded  to  the  cable  for  the  purpose  of  shunting 
stray  currents  which  otherwise  would  flow  through  the  sheath  of  the  cable. 

Satisfactory  operation  of  electric  railroads  requires  that  adequate  bond- 
ing between  abutting  rails  be  maintained  in  order  that  the  circuit  resistance 

1  Where  this  method  of  thawing  water-pipes  is  practised  it  has  been  found  that  neigh- 
boring pipe  systems  are  endangered  to  an  extent  dependent  upon  the  proximity  of  such 
lines  to  the  water-pipes  being  treated,  upon  the  character  of  the  sub-soil,  and  upon  the 
electrical  continuity  of  any  intervening  joints  in  the  water-pipe  between  the  points  upon 
their  surfaces  where  the  thawing  current  is  applied. 


470  AMERICAN  TELEGRAPH  PRACTICE 

between  the  negative  terminals  of  car  motors  and  the  negative  terminal  of 
the  power  generator  will  be  as  low  as  possible,  and  unless  the  condition  of 
all  bonds  is  constantly  inspected,  high-resistance  contacts  are  liable  to  develop 
and  remain  undetected  until  considerable  damage  has  been  done  to  adjacent 
cable  sheaths.  So  far  as  rail  bonding  is  concerned  it  should  be  remembered 
that  the  conductivity  of  copper  is  about  ten  times  that  of  the  steel  used  in 
making  the  rails,  the  copper  bond  employed  should,  therefore,  be  of  one- 
tenth  the  sectional  area  of  the  rail  if  the  bond  is  to  have  the  same  current- 
carrying  capacity  as  the  rail. 

Where  two  or  more  cables  terminate  in,  or  pass  through  a  manhole  the 
various  cables  should  be  bonded  together,  preferably  with  a  strip  of  lead  2  or 
3  in.  in  width.  Where  lead  is  used  in  cable  to  cable  bonding  there  is  less 
likelihood  of  galvanic  action  than  where  copper  bonds  are  used. 

Where  cable  sheaths  are  found  to  be  positive  to  track  rails,  it  is  customary 
to  bond  the  cable  to  the  rails,  and  while  there  are  certain  objections  to  this 
practice  and  some  risk  incurred,  the  general  experience  is  that  the  advantages 
outweigh  the  disadvantages. 


APPENDIX  A 
REFERENCES  TO  PRINTING  TELEGRAPH  LITERATURE 

1.  THE  BRETT  PRINTING  TELEGRAPH,  "  The  Telegraph  Manual,"  Shaffner, 

1859,  page  273. 

2.  THE  BONELLI  TYPO-TELEGRAPH,  " Electricity  and  the  Electric  Tele- 

graph," Prescott,  1888,  page  763. 

3.  THE  BUCKINGHAM  PRINTER,  "American  Telegraphy,"  Maver,  page  436a. 

4.  THE  BARCLAY  PRINTING  TELEGRAPH  SYSTEM,  Serial  Article  by  William 

Finn,  in  Telegraph  Age,  N.  Y.,  running  from  June  16,  1908,  to 
March  i,  1909. 

5.  THE  BURRY  PRINTER,  Telegraph  Age,  N.  Y.,  April  i,  1903,  page  169. 

6.  THE  BAUDOT  PRINTING  TELEGRAPH  SYSTEM,  "The  Hughes  and  Baudot 

Telegraphs,"  Crotch.     Rentell  &  Co.,  London,  1908. 

7.  THE  CARD  WELL  PRINTING  TELEGRAPH  SYSTEM,  Telegraph  Age,  N.  Y., 

June  i,  1905,  page  221. 

8.  THE  "COMBINATION"  TELEGRAPH  PRINTER,  "Electricity  and  the  Elec- 

tric Telegraph,"  Prescott,  1888,  page  608. 

9.  THE  CREED  TELEGRAPH  PRINTER,  Electrical  Review,  London,  Sept.  25, 

1908.  Electrical  Review,  London,  Dec.  4,  1908.  Telegraph  Age, 
New  York,  July  i,  1907. 

10.  THE  DEAN  PRINTING  TELEGRAPH  SYSTEM,  Telegraph  Age,  N.  Y.,  Aug. 

16,  1907,  page  443. 

11.  THE  ESSICK  PRINTER,  "American  Telegraphy,"  Maver,  page  431. 

12.  THE  HOUSE  PRINTING  TELEGRAPH,  "The  Electromagnetic  Telegraph," 

Lardner,  1853,  page  117.  "History,  Theory,  and  Practice  of  the 
Electric  Telegraph,"  Prescott,  1864,  page  in.  "Electricity  and  the 
Electric  Telegraph,"  Prescott,  1888,  page  604. 

13.  THE  HUGHES  PRINTING  TELEGRAPH,  "History,  Theory  and  Practice  of 

the  Electric  Telegraph,"  Prescott,  1864,  page  139.  "Electricity 
and  the  Electric  Telegraph,"  Prescott,  1888,  page  608. 

14.  THE    HUGHES    TYPE-PRINTING    TELEGRAPH    SYSTEM,    "Telegraphy," 

Herbert,  1906,  page  370.  "Hughes  Type-printing  Telegraph 
System,"  Wyman  &  Sons,  London,  1906. 

15.  THE  MORKRUM  PRINTING  TELEGRAPH,  Telegraph  Age,  N.  Y.,  June.  16, 

1912. 

16.  THE  MURRAY  PRINTING  TELEGRAPH  SYSTEM,  "Telegraphy,"  Herbert, 

1906,  page  826. 

471 


472  AMERICAN  TELEGRAPH  PRACTICE 

17.  THE  PHELPS  TYPE-PRINTING  TELEGRAPH,  "  Electricity  and  the  Electric 

Telegraph,"  Prescott,  1888,  page  736. 

18.  THE    PHELPS    MOTOR    PRINTER,     "American    Telegraphy,"    Maver, 

page  4i9b. 

19.  THE    ROWLAND   PRINTING   TELEGRAPH    SYSTEM,    Proceedings   of   the 

American   Institute   of   Electrical   Engineers,   Vol.   XXVI,    1907, 
page  507. 

20.  SIEMENS  TYPE-PRINTING  TELEGRAPH.  "  Electricity  and    the    Electric 

Telegraph,"  Prescott,  1888,  page  734. 

21.  THE  WRIGHT  PRINTER,  Telegraph  Age,  N.  Y.,  May  16,  1910,  page  348. 


APPENDIX  B 

SPECIFICATIONS  FOR  THE  CONSTRUCTION  OF  HIGH-TENSION 
POWER  TRANSMISSION  LINES  ABOVE  TELEGRAPH  WIRES1 

GENERAL 

(a)  These  specifications  apply  to  constant-potential  power  transmission 
lines  of  over  5,000  volts. 

(b)  These  specifications  prescribe  a  certain  minimum  standard  of  con- 
struction for  the  high-tension  line  which  is  required  in  order  to  provide  a 
reasonable  degree  of  security  against  the  failure  of  any  portion  of  the  high- 
tension  construction  that  might  allow  the  high-tension  wires  to  come  into 
contact  with  the  telegraph  wires. 

(c)  It  is  not  the  purpose  of  these  specifications  to  restrict  the  high-tension 
construction  narrowly  in  details,  but  to  stipulate  the  fundamental  principles 
which  must  be  followed  in  order  to  attain  reasonable  safety. 

(d)  Each  portion  of  the  high-tension  line  shall  have  sufficient  strength  to 
resist  the  maximum  mechanical  stresses  to  which  it  may  be  subjected,  due 
allowance  being  made  for  a  factor  of  safety  suited  to  the  degree  of  uniformity 
of  the  material,  the  character  of  the  material  with  respect  to  deterioration 
and  the  nature  of  the  stress,  as  hereinafter  specified. 

(e)  Obviously  the  maximum  mechanical  loads  upon  the  high-tension  con- 
struction will  usually  occur  when  the  wires  are  coated  with  ice  and  subjected 
to  the  maximum  wind  velocity  at  right  angles  to  the  line  at  the  minimum 
temperature. 

(f)  The  maximum  stresses  in  the  high-tension  construction  shall  be  com- 
puted on  the  basis  of  a  wind  pressure  of  20  Ib.  per  square  foot  of  plane  area, 
or  12  Ib.  per  square  foot  of  projected  area  for  cylindrical  surfaces.     These 
values  are  based  upon  a  maximum  actual  wind  velocity  of  70  miles  per  hour 
and  are  to  be  used  in  connection  with  the  following  coincident  conditions : 

(1)  Maximum  coating  of  ice,  1/2  in.  in  thickness. 

(2)  Minimum  temperature,  zero  degrees  Fahrenheit. 

NOTE. — In  a  few  sections,  in  southern  portions  of  the  country,  minimum 
temperatures  of  zero  degrees  and  ice  formation  are  not  encountered.  For 
transmission  lines  constructed  in  such  regions  the  above  requirements  may  be 
suitably  modified  to  accord  with  local  climatic  conditions.  In  no  case  shall 
the  minimum  temperature  be  taken  above  30°  F. 

1  From  Standard  Specifications. 

473 


474  AMERICAN  TELEGRAPH  PRACTICE 

(g)  The  general  types  of  construction  which  shall  be  employed,  the  factors 
of  safety  to  be  observed,  and  the  minimum  sizes  and  strengths  of  materials, 
shall  be  as  specified  below. 

(h)  Where  galvanizing  of  iron  or  steel  is  required,  it  shall  conform  to  the 
requirements  of  the  appended  specifications  for  galvanizing  for  iron  and  steel. 

TOWERS  AND  POLES 

(1)  Material. — The  poles  supporting  the  high-tension  conductors  where 
these  are  above  the  telegraph  line  shall  preferably  be  of  steel.     Reinforced 
concrete  or  wood  poles  may  be  employed  under  suitable  restrictions  as  herein- 
after specified. 

(j)  Factors  of  Safety. — (i)  Poles  shall  have  the  following  minimum  fact- 
ors of  safety  according  to  the  nature  of  the  materials  employed: 

Steel 3 

Reinforced  concrete 4 

Completely  creosoted  wood 5 

Other  wood 6 

(2)  The  poles,  at  the  terminals  of  the  portion  of  the  high-tension  line  cov- 
ered by  these  specifications,  shall  be  of  such  strength  as  not  to  break  under  the 
maximum  load  conditions,  if  any,  or  all,  of  the  conductors  in  the  spans  outside 
this  portion  should  break. 

(k)  Wood  or  Reinforced  Concrete  Poles. — (i)  Wood  poles  shall  not  be 
used  where  inflammable  materials,  such  as  structures,  are  situated  within  a 
distance  sufficient  to  cause  an  appreciable  fire  hazard  to  the  pole. 

(2)  If  wood  poles  are  employed,  surrounding  underbrush  and  grass  must 
be  removed  for  a  sufficient  distance  to  avoid  fire  hazard. 

(3)  Wood  or  reinforced  concrete  poles  must  be  provided  with  a  grounded 
copper  wire  or  an  approved  equivalent  metal  strip,  placed  at  the  side  of  the 
pole  and  extended  to  the  top  of  the  pole  and  over  the  top  of  the  pole.     In 
the  case  of  wood  poles  this  grounded  conductor  shall  be  extended  down  the 
opposite  side  of  the  pole  to  the  top  of  the  lowest  cross-arm,  Fig.  419.     This 
grounded  conductor  shall  be  of  sufficient  conductivity  to  carry  safely  the 
maximum  short-circuit  current.     This  grounded  conductor  provides  lightning 
protection  and,  in  the  case  of  wooden  poles,  serves  to  prevent  arcing  and 
setting  fire  to  the  pole  in  case  a  high-tension  wire  becomes  detached  from  its 
insulator  and  rests  against  the  side  of  the  pole. 

(1)  Guys. — (i)  Where  guys  can  be  placed,  the  total  strength  of  the 
guyed  structure  shall  be  sufficient  to  sustain  the  maximum  stress  with 
factors  of  safety  not  less  than  those  specified  in  section  (j). 

(2)  All  guys  shall  be  anchor  guys,  guys  to  anchored  stubs  or  rock  guys. 

(3)  Methods  of  anchoring,  locations  for  anchors,  and  depth  and  character 
of  setting  shall  be  such  as  to  render  effective  the  full  strength  of  the  guy. 


APPENDIX  B 


475 


(4)  Guys  shall  be  of  galvanized  steel  strand  not  smaller  than  five-six- 
teenths in.  in  diameter. 

(5)  Strain  insulators  are  not  required,  but  if  these  should  be  placed  in 
guys,  each  strain  insulator  shall  have  a  breaking  strength  not  less  than  that 
of  the  guy  in  which  it  is  placed.     Every  guy  which  passes  over  or  under  any 
electric  wires,  other  than  these  carried  upon  the  guyed  pole  shall  be  so 
placed  and  maintained  as  to  provide  at  all  times  a  clearance  of  not  less  than 
2  ft.  between  the  guy  and  such  electric  wire. 

(m)  Minimum  Size  Wood  Poles. — No  wood  pole,  whether  guyed  or  not, 
shall  be  less  than  8  in.  in  diameter  at  the  top. 


a     A     a 


ft ft 


Not  less  than 
^Galvanized 
Strand— -y 


^-Galvanized 
/          IronStr/ps 
*    ft 


FIG.  419. 

(n)  Replacement  of  Wood  Poles.— Wood  poles  shall  be  periodically 
inspected  and  shall  be  replaced  before  their  strength  falls  below  two-thirds 
of  their  initial  strength. 

(o)  Structural  Steel  Poles  or  Towers. — (i)  All  structural  steel  shall 
conform  to  specifications  for  open-hearth  railway  bridge  or  medium  steel 
adopted  by  the  Association  of  American  Steel  Manufacturers. 

(2)  All  steel  poles  and  towers  shall  either  be  galvanized  or  thoroughly 
painted  with  not  less  than  three  coats  of  an  approved  metal  preservative. 


476  AMERICAN  TELEGRAPH  PRACTICE 

Painting  shall  consist  of  at  least  one  shop  coat  and  two  field  coats,  preferably 
all  of  different  shades  of  color. 

(3)  Steel  poles  and  towers  shall  be  thoroughly  grounded  in  a  manner 
satisfactory  to  the  telegraph  company. 

(p)  Unit  Strength  of  Materials. — The  fiber  stresses  to  be  employed  in 
computing  the  strengths  of  poles  shall  not  be  more  than  as  follows: 

Working  fiber  stress 

(  medium 20,000  Ib. 

\  railway  bridge 18,500  Ib. 

Cedar 600  Ib. 

Chestnut 800  Ib. 

Creosoted  yellow  pine 1,200  Ib. 

The  working-fiber  stresses  given  above  include  allowances  for  factors 
of  safety  in  accordance  with  the  preceding  requirements. 

(q)  Setting  Poles. — (i)  Great  care  shall  be  taken  in  setting  poles  at 
high-tension  crossings  to  secure  firm  foundations. 

(2)  Exposure  to  washouts  shall  be  avoided. 

(3)  Poles  shall  not  be  set  on  sloping  banks  when  other  location  is  practi- 
cable.    Where  poles  are  necessarily  set  on  sloping  banks  they  shall  be  well 
reinforced  by  cribbing. 

(4)  In  sandy  or  swampy  soil  concrete  foundations  shall  be  provided 
for  wood  poles.     Each  foundation  shall  contain  not  less  than  two  cubic 
yards  of  concrete. 

(5)  Concrete  shall  not  be  leaner  than  one  part  of  cement  to  two  and 
one-half  parts  of  sand,  to  five  parts  of  broken  stone.     An  equivalent  gravel 
concrete  may  be  used.     Cement  shall  be  Portland  cement  conforming  to  the 
standard  specifications  of  The  American  Society  for  Testing  Materials. 
Sand  shall  be  clean  and  sharp.     All  concrete  shall  be  mixed  and  placed 
thoroughly  wet. 

WIRES 

(r)  Spans  Covered  by  these  Specifications,  (i)  Crossings. — The  con- 
struction herein  specified  applies  to  the  cross-over  span.  Where  the  distance 
from  the  topmost  high-tension  wire  at  either  pole  of  the  cross-over  span  to 
the  nearest  wire  on  the  telegraph  line  is  less  than  one  and  one-half  times  the 
height  of  the  topmost  high-tension  wire  above  the  ground  at  the  high-tension 
pole,  the  requirements  specified  for  the  cross-over  span  shall  be  considered 
as  applying  also  to  the  next  high-tension  span  adjacent  to  that  pole,  Fig.  420. 

(2)  Parallel  Lines. — Where  the  high-tension  line  must  necessarily  be 
constructed  higher  than  and  parallel  to  the  telegraph  line,  and  separated 
from  the  latter  by  a  distance  less  than  the  height  of  the  high-tension  poles, 
the  construction  shall  conform  to  the  requirements  for  the  cross-over  span 


APPENDIX  B 


477 


as  herinafter  specified.  The  requirements  shall  also  apply  to  each  span  next 
adjacent  to  the  portion  above  the  telegraph  line,  unless  the  distance  from  the 
nearest  telegraph  wire  to  the  topmost  high-tension  wire  on  the  high-tension 
poles  at  the  end  of  the  over-built  section,  is  greater  than  one  and  one-half 
times  the  height  of  the  topmost  high-tension  wire  from  the  ground,  Fig.  421. 
(s)  Factors  of  Safety. — The  length  of  the  cross-over  span  and  the  sag  of 
the  wire  shall  be  so  proportioned,  with  reference  to  the  kind  and  size  of  wire 


\ 

vq 

\ 

£ 

a    a    e    e    gf~'' 

1 

• 

^ 

, 

h 

-%• 

w^      -^f 

~ 

/                                                                                                                                     '// 

'  ^ 

*uu 

: 

Note:                               *  ( 
If  "a  "is  less  than  1^  times  "h  " 
the  Requirements  for  the  Cross- 
over Span  shall  apply  also  to  the 
adjacent  Span. 

FIG.  420. 


and  method  of  suspension,  that  a  factor  of  safety  of  at  least  2,  and  no  stresses 
beyond  the  elastic  limit  of  the  material  will  be  obtained  under  the  maximum 
conditions  specified  in  clause  (f). 

(t)  High-tension  Conductors. — (i)  Stranded  wire  shall  be  used  for  the 
high-tension  conductors  in  the  cross-over  span  and  other  spans  covered  by 
the  requirements  of  these  specifications.  Each  shall  consist  of  not  less  than 
seven  component  wires. 

(2)  The  minimum  sizes  of  conductors  shall  be 


Copper 

Aluminum. . 


Not  less  than  No.    o  B.  &  S.  gage. 
Not  less  than  No.  oo  B.  &  S.  gage. 


(3)  There  shall  be  no  joints  in  the  conductors  in  the  spans  requiring 
special  construction. 

(u)  Precautions  against  Injury  to  Wires  from  Arcing,  (i)  Separation. 
— The  minimum  separation  between  wires  on  centers  shall  be  as  follows: 


478 


AMERICAN  TELEGRAPH  PRACTICE 


M 


APPENDIX  B 


479 


Voltage  between  wires 

Minimum  separation  on 
centers 

Under  1  2  tjoo 

2      ft. 

1  2  500  to  10  ooo                                    

2^  ft. 

20  ooo  to  20  ooo                                                      •  •            

3!  ft. 

•?o  ooo  to  30  ooo 

4     ft. 

40  ooo  to  50  ooo                                      

5    ft. 

60  ooo  and.  over                                                              

6    ft. 

(2)  At  Insulators. — (i)  At  the  poles  forming  the  termini  of  the  spans 
covered  by  these  specifications,  each  conductor  shall  be  so  protected  at  the 
point  of  attachment  to  the  insulator,  that  if  the  insulator  breaks  down  elec- 
trically, the  resulting  arc  will  not  burn  the  conductor.  This  may  be  accom- 
plished by  providing  between  the  conductor  and  the  insulator  a  metal  cap 
which  will  interpose  at  least  1/2  in.  of  metal  between  the  line  conductor  and 
the  head  of  the  insulator.  Also  the  conductor  shall  be  protected  from  an  arc 
for  a  distance  of  not  less  than  24  in.  on  each  side  of  the  center  of  the  insulator 
head  by  a  serving  of  wire  or  a  sheet  metal  envelope  not  less  than  No.  6  B.  &  S. 
gage  in  thickness. 

(2)  The  wire  serving  or  sheet  metal  envelope  shall  be  of  the  same  kind 
of  metal  as  the  line  conductor  which  it  protects. 

(v)  Minimum  Clearance  above  Telegraph  Wires. — The  high-tension 
construction  shall  be  such  that  at  a  temperature  of  130°  above  the  minimum 
temperature  (clause  F.),  the  lowest  high-tension  wire  shall  clear  the  highest 
telegraph  wire  or  cable  by  not  Jess  than  8  ft.  Where  practicable,  no  telegraph 
pole  shall  be  closer  than  1 5  ft.  horizontally  to  the  nearest  high-tension  wire. 
The  telegraph  crossarms  may  be  spaced  15  in.  on  centers  at  crossings  in 
order  to  allow  high-tension  poles  of  minimum  height  to  be  used. 

(w)  Unit  Strength  and  Elasticity  of  Materials. — (i)  The  tensile  strengths 
to  be  employed  in  computing  the  wires  shall  not  be  more  than  as  follows: 


Working    strength, 
pounds  per  square  inch 

Hard-drawn  copper  stranded  conductor  
Hard-drawn  aluminum  stranded  conductor  

30,000 

12  OOO 

(2)  The  modulus  of  elasticity  may  be  taken  as  follows: 


480  AMERICAN  TELEGRAPH  PRACTICE 


Modulus  of  elasticity 

Hard-drawn  copper  stranded  conductor  •  
Hard-drawn  aluminum  stranded  conductor  
Steel  strand  

12,000,000 
7,500,000 

22  OOO  OOO 

(x)  Coefficient  of  Linear  Expansion. — The  coefficient  of  linear  expansion 
per  Fahrenheit  degree  may  be  taken  as  follows: 

Copper o .  0000096 

Aluminum o .  0000130 

Steel o .  0000064 

(y)  Method  of  Attachment. — In  all  spans  covered  by  these  specifications, 
the  high-tension  conductors  shall  be  attached  to  the  insulators  on  each  side  of 
the  span  by  mechanical  clamps  or  approved  ties.  Ties  such  as  are  ordinarily 
employed  for  signaling  wire  shall  not  be  used.  The  clamps  or  ties  shall  have 
sufficient  grip  and  shall  be  set  up  sufficiently  tight  so  as  to  hold  the  conductors 
up  to  stresses  equal  to  the  working  strengths  of  the  conductors  and  shall  be 
of  such  a  design  as  not  to  injure  the  wire.  If  ties  are  used,  the  tie  wires  shall 
be  attached  to  the  line  conductor  at  a  distance  from  the  head  of  the  insulator 
not  less  than  one- tenth  of  the  distance  specified  in  section  (u),  and  in  no  case 
less  than  4  in. 

CROSSARMS 

(z)  Material. — The  crossarms  supporting  the  wires  or  strands  shall  be  of 
steel  or  creosoted  wood. 

(aa)  Factors  of  Safety. — Crossarms  shall  have  the  following  minimum 
factors  of  safety  according  to  the  nature  of  the  material  employed: 

Steel 3 

Creosoted  wood 5 

(bb)  Loads  on  Crossarms. — The  crossarm  and  its  attachment  shall  have 
sufficient  strength  to  provide  against  breaking,  in  the  case  of  the  breaking  of 
any  or  all  of  the  wires  in  the  span  adjacent  to  the  cross-over  span. 

(cc)  Steel  Crossarms. — Steel  crossarms  should  preferably  be  used.  Steel 
crossarms  shall  be  thoroughly  grounded.  All  portions  of  the  ground  connec- 
tion shall  have  sufficient  conductivity  to  carry  safely  the  maximum  short- 
circuit  current. 

(dd)  Wood  Crossarms. — (i)  If  wood  crossarms  are  employed  they  shall 
be  treated  with  creosote  or  dead  oil  of  coal  tar  in  accordance  with  approved 
specifications. 


APPENDIX  B  481 

(2)  Wood  crossarms  shall  be  provided  with  grounded  galvanized  iron 
plates  or  grounded  copper  wires  on  their  upper  surfaces.  Plates  shall  not  be 
less  than  1/4  of  an  inch  in  thickness,  and  of  a  cross-sectional  area  not  less  than 
that  of  the  ground  wire.  If  copper  wires  are  employed  they  shall  be  of  suffi- 
cient conductivity  to  carry  safely  the  short-circuit  current.  Ground  wires 
or  plates  shall  be  firmly  attached  to  the  crossarms. 

(ee)  Protection  of  Metal  from  Corrosion. — All  portions  of  steel  crossarms 
and  their  fittings,  and  the  center  bolts,  braces,  ground  plates  and  other 
fittings  of  wood  crossarms  shall  be  thoroughly  galvanized. 

(ff )  Protection  Against  Line  Conductors  Falling  Clear  of  Crossarms. — At 
spans  where  these  specifications  apply,  angles  in  the  route  of  the  high-tension 
line  shall  be  avoided  wherever  practicable.  At  these  spans,  if  mechanical 
clamps  are  not  employed,  the  outer  high-tension  line  conductors  shall  in  all 
cases  be  attached  so  as  to  pull  against  the  insulators. 

PINS 

(gg)  Material. — Steel  pins  shall  be  used. 

(hh)  Strength  of  Pins. — Pins  shall  be  sufficiently  strong  to  provide  a 
factor  of  safety  of  3  against  stresses  produced  by  the  maximum  wind  pres- 
sure on  the  wires  loaded  with  ice  and  also  against  stresses  produced  by  the 
breaking  of  the  wire  in  the  span  adjacent  to  the  crossing  span. 

(ii)  Grounding  of  Pins. — Pins  shall  be  thoroughly  grounded. 

INSULATORS 

(jj)  Material. — Porcelain  insulators  shall  be  used  for  supporting  the  high- 
tension  conductors. 

(kk)  Mechanical  Strength.— The  insulators  shall  be  sufficiently  strong 
so  that,  when  mounted,  they  shall  be  able  to  withstand  without  injury  twice 
the  maximum  mechanical  stress  to  which  they  will  be  subjected  with  the  line 
conductors  attached  as  herein  specified. 

(11)  Dielectric  Strength. — Where  tested  under  approved  methods  each 
insulator  shall  be  capable  of  resisting  three  times  the  normal  voltage  when 
tested  dry  and  twice  the  normal  voltage  under  spray  test. 

(mm)  Disk  Insulators. — Where  suspension  insulators  are  used,  each 
individual  disk  shall  be  provided  with  interlinked  attachments  so  that,  in 
case  the  porcelain  should  be  shattered,  the  conductor  would  remain  mechanic- 
ally attached  to  the  crossarm.  The  support  next  adjacent  to  the  crossarm 
shall  be  thoroughly  grounded. 

LIGHTNING  PROTECTION 

(nn)  Each  pole  and  tower,  in  the  portion  of  the  high-tension  line  covered 
by  these  specifications,  shall  be  provided  with  a  grounded  lightning-protec- 
tive device  extending  above  the  top  of  the  pole  or  tower  and  not  less  than  3  ft. 
above  the  highest  conductor. 

31 


482 


AMERICAN  TELEGRAPH  PRACTICE 


CONSTANTS,  UNIT  STRESSES  AND  FORMULAE  TO  BE  USED  IN  COMPUTING 
STRENGTH  OF  TRANSMISSION  LINES 

UNIT  STRESSES 
POLES  AND  TOWERS 


Allowable  working  fiber  stress 


Steel.  . 


medium 

railway  bridge. 

Cedar 

Chestnut 

Creosoted  yellow  pine . .  . 


20,000  Ib.  per  square  inch. 
18,500  Ib.  per  square  inch. 

600  Ib.  per  square  inch. 

800  Ib.  per  square  inch. 
1,200  Ib.  per  square  inch. 


WIRE  AND  STRAND 


Allowable  tensile  strength 


Stranded  copper. . .  . 
Stranded  aluminum. 
Steel  strand. . 


30,000  Ib.  per  square  inch. 
12,000  Ib.  per  square  inch. 
(According  to  the  character  of  the 

material,    a   factor  of  3    being 

used). 


Modulus  of  elasticity 


Stranded  copper.  . .  . 
Stranded  aluminum. 
Steel  strand. . 


12,000,000 

7,500,000 

22,000,000 


Coefficient  of  linear  expansion 
per  degree  Fahr. 


CoDoer 

o  .  0000096 

Aluminum                                                                     .    .  . 

o.  0000130 

Steel 

o  .  0000064 

APPENDIX  B  483 

CROSSARMS 


Allowable  working  fiber  stresses 


Steel. 


medium 

railway  bridge. 
Creosoted  yellow  pine 


20,000  Ib.  per  square  inch, 

18,500  Ib.  per  square  inch. 

1,200  Ib.  per  square  inch. 


PINS 


Allowable  working  fiber  stress 


Steel. 


20,000  Ib.  per  square  inch. 


Wind  Pressure.— 

P=  pressure  in  pounds  per  square  foot. 

7  =  actual  velocity  of  wind  in  miles  per  hour. 
For  plane  surfaces 

P  =o.oo4F2. 
For  cylindrical  surfaces 

P  =0.002572 

(P  =  pressure  per  square  foot  of  projected  area.) 
For  velocity  of  70  miles  per  hour 

P  =20  Ib.  for  plane  surfaces. 

P  =12  Ib.  for  cylindrical  surfaces. 
Sleet  and  Ice. — 

Weight  of  ice  per  cubic  foot,  58  Ib. 

Weight  of  block  of  ice  i  ft.  long  and  rsq.  in.  section,  0.403  Ib. 
Poles. — A  pole  is  essentially  a  beam  fixed  at  one  end.     The  ordinary 
beam  formulae  apply. 

The  strength  of  a  pole  is  given  by  the  formula 

M+£ 

y 

where  M  =  moment  of  the  forces  about  the  ground  line  (or  other  point  at 
which  the  strength  is  being  considered) . 

p  =  maximum  fiber  stress. 

/  =  moment  of  inertia  of  section  of  pole. 

y  =  distance  from  center  to  most  strained  fiber. 
For  a  pole  of  circular  cross-section 


484  AMERICAN  TELEGRAPH  PRACTICE 

where  D  =  the  diameter  of  the  pole  in  inches  and  the  moment  arms  of  the 
forces  are  expressed  in  feet. 

p  is  the  maximum  ultimate  fiber  stress  or  the  allowable  working  fiber 
stress  according  as  the  ultimate  strength  or  safe  working  strength  of  the  pole 
is  desired. 

Forces  Acting  on  a  Pole  Transversely.— 
Wing  pressure  on  pole. 
Wing  pressure  on  conductors. 

The  approximate  moment  at  the  ground  due  to  wind  pressure  on  the  pole 
would  be 

^ 


72 

P      =  wind  pressure  per  square  foot  of  projected  area. 
H     =  height  of  pole  above  ground  in  feet. 
DI    =  diameter  of  pole  at  ground. 
D2    =  diameter  of  pole  at  top. 
The  moment  at  the  ground  due  to  wind  pressure  on  the  wires  would  be 


24 

L     =  height  of  wires  above  ground  in  feet. 

n     =  number  of  wires. 

Di    =  diameter  of  conductor  loaded  with  ice. 

Si    =  and  Sz  =  lengths  of  adjacent  spans  in  feet. 

The  total  moment  is  the  sum  of  M P,  Mci,  Mc2,  etc. 

Conductors. — A  metallic  conductor  is  elastic  and  also  expands  and  con- 
tracts with  changes  in  temperature.  When  a  wire  in  a  span  is  cooled  it 
contracts,  making  the  sag  less  and  increasing  the  tension  in  the  wire.  The 
elongation  of  the  wire  due  to  the  increased  tension  tends  to  increase  the 
sag  and  to  diminish  the  tension.  When  a  wire  is  loaded  by  sleet  or  by  wind 
pressure  the  increased  tension  in  the  wire  causes  it  to  stretch  and  the  sag  to 
increase.  The  increase  in  the  sag  tends  to  reduce  the  tension. 

The  formulae  for  computing  these  various  changes  are  as  follows: 

Relation  between  temperature  and  sag 

81     fJ  2     j  2\  ,  T  T  P  v 

d, 


where  sag  and  span  are  expressed  in  feet. 


where  sag  is  in  inches  and  span  in  feet. 


APPENDIX  B  485 

Symbols. — 

a    =  temperature  variation  for  small  changes  in  sag. 
/o  =  initial  temperature. 


F  =  length  of  span. 

do  =  sag  at  temperature  to. 

di  =sag  at  temperature  t\. 

c    =  coefficient  of  linear  expansion  per  degree  F. 

e    =  modulus  of  elasticity. 

p    =load  per  foot  of  wire. 

s    =  cross-section  of  wire  in  square  inches. 

By  assuming  small  changes  in  the  sag,  successive  values  of  a  may  be 
found  from  which  a  curve  showing  the  variation  of  sag  with  temperature 
may  be  made. 

Relation  between  tension  and  sag. 

pY2 
T=  --g-j-  (sag  and  span  in  feet) 

Length  of  wire. — 

(8  d2\ 
iH —  TFs)  (span  and  sag  in  feet) 
O 

Elongation  due  to  change  in  tension. 
TL 

~  es 

Example. — Poles: 

Length  of  pole,  40  ft. 
Height  of  pole  above  ground,  34  ft. 
Length  of  adjacent  spans,  100  ft.  and  120  ft. 
Wires: 

One  No.  o  wire  on  top  of  pole. 
Two  No.  o  wires  on  crossarm  3  ft.  below  top. 

Two  No.  12  telegraph  wires  on  crossarm  7  ft.  below  lower  power 
wires. 

To  find  dimensions  of  cedar  pole  to  give  factor  of  safety  of  6  with  a  wind 
velocity  of  70  miles  in  a  direction  at  right  angles  to  the  line  and  1/2  in. 
thickness  of  ice  on  each  wire. 
Wind  pressure  on  upper  wire. 

Diameter  of  No.  o  wire  =  0.37. 

Diameter  of  No.  o  wire  covered  with  1/2  in.  ice  =  1.37. 
^PLnDj  (5t+5a) 

24 

_  12.3X34X1X1.37(100+120)  _ 
MCl~  ~2^T  -5,253- 


486  AMERICAN  TELEGRAPH  PRACTICE 

Wind  pressure  on  two  middle  wires: 

12.3X31X2X1.37(100+120) 
Mc2  =  -  ~  =  9>579- 

Wind  pressure  on  telegraph  wires: 

Diameter  of  No.  12  wire  =  0.104  in. 

Diameter  of  No.  12  wire  covered  with  1/2  in.  ice  =  1.104  m- 

12.3X24X2X1.104(100+120) 
Mcs=  —^-  -  =  5,975- 

Wind  pressure  on  pole  assuming  diameters  at  butt  and  top  to  be  17  in. 
and  8  in. 


, 
6,500 


I2-3X342X33- 


(If  the  result  gives  dimensions  of  poles  much  different  from  the  values 
assumed  a  second  approximation  should  be  made.) 
Total  moment  =  27,307 


For  cedar  p  =  600 

6007TZV 


4.91  Z>13  =  27,307 

1)1=17.1  in. 

Circumference  at  ground  line  =  54*  in. 

Example.  —  Conductors:  To  find  sag  of  wire  at  60°  F.  such  that  the  wire 
will  have  a  factor  of  safety  of  2  at  o°  F.  with  ice  1/2  in.  thick  all  around  the 
wire  and  wind  blowing  at  right  angles  to  the  line  at  a  velocity  of  70  miles  an 
hour. 

Size  of  wire  No.  o. 
Wire  of  stranded  copper. 
Length  of  span  200  ft. 
Diameter  of  wire  =  0.370  in. 
Cross-section  of  copper  =  0.083  scl-  m- 
Diameter  of  wire  +  1/2  in.  ice  =  1.370  in. 
Cross-section  of  wire  +1/2  in.  ice  =  1.47  sq.  in. 
Cross-section  of  ice  =  1.39  sq.  in. 
Weight  of  wire  per  foot  =  0.323  Ib. 


APPENDIX  B 


487 


Weight  of  ice  per  foot  =  0.403X1.39  =  0.560  Ib. 

Weight  of  ice  and  wire  per  foot  =  0.560+0.323=0.883  Ib. 


1.370 
Wind  pressure  per  foot  =  ----  X  12.  3  =  1.40 


Ib. 


Resultant  pressure  per  foot  =  V  i.4o2  +  o.8832  = 

Breaking  weight  of  No.  o  wire  =  4,980  Ib. 

With  factor  of  safety  of  2,  the  allowable  tension  in  the  wire  = 

2,490  Ib. 
At  o°  the  wires  weighted  with  wind  and  ice 


d  = 


sr 

1.65X40000 
8X2490 


^  =  3.3  ft. 
With  sag  of  3.3  ft.  the  length  of  wire 


200(1  +  3 


Contraction  due  to  removal  of  wind  and  ice  : 

TL 


E  = 


es 


200.145 


1 2000000  X  0.083 

=  0.000201  T  (T  in  this  case  being  the  differ 
ence  in  tension.) 


Tension 

Length 

Sag 

2,490 

200.  145 

3-3 

2,39° 

200.  125 

3-o6 

2,290 

200.  105 

2.80 

2,190 

200.085 

2.52 

2,090 

200.065 

2.21 

1,990 

200.045 

1.84 

1,890 

200.025 

i-37 

1,790 

200.004 

0-55 

488  AMERICAN  TELEGRAPH  PRACTICE 

The  sag  for  each  of  the  above  lengths  is  determined  from  the  formula; 


=  8.65  \/L  —  200 
Increase  in  tension  due  to  contraction  of  wires: 

wY2 


"If 

0.323  X  40000 

ST 

1615 
T 

Tension 

Sag      * 

1,615 

I.O 

1,700 
i,  800 
1,900 

o-95 
0.9 
0.85 

Plotting  these  two  relations  of  tension  and  sag  with  sags  as  abscissae  and 
tensions  as  ordinates,  the  intersection  of  the  two  curves  shows  the  sag  and 
tension  at  equilibrium. 

From  the  curve: 

Sag  =  0.89  ft.  =  10.7  in. 
Tension  =  1,820  Ib. 

Which  represents  the  conditions  in  the  wire  at  o°  F.  without  wind  or  sleet. 
To  find  the  sags  at  other  temperatures: 

4  1        °       2  ec  s         dn    d* 


54 


54  cY2     54X0.0000096X40000 


=  0.0482 


2  ec  s 


APPENDIX  B 


489 


Assume  variations  of  i  in.  in  the  sag, 
^0=10.7  in.  ^1  =  11.7  in. 

a   =    0.0482    (22.4)  +  202oX 

=   1.08+16.20  =  17.30 


I7-30 


^0=11  •  7  in. 

0  =  14.8 

32.1 

12.7 

12.9 

45-o 

13-7 

11.4 

56-4 

14-7 

10.2 

66.6 

15-7 

9-3 

75-9 

16.7 

8-5 

84.4 

17.7 

7-9 

92-3 

18.7 

7-3 

99.6 

19.7 

6.Q 

106.5 

20.7 

6.6 

113.1 

21.7 

6.2 

H9-3 

22.7 

6.0 

125.3 

Plotting  with  sags  as  abscissae  and  temperatures  as  ordinates,  the  sag 
at  any  temperature  can  be  read  from  the  curve;  for  example,  the  sag  at  60° 
should  be  15  in. 


SAG  OF  WIRES  • 

Tables  showing  the  sag  at  ordinary  ranges  of  temperature  for  various 
sizes  of  stranded  copper  and  aluminum  wire  to  give  a  factor  of  safety  of  2 
at  o°  F.  under  conditions  of  70  miles  per  hour  wind  velocity  and  1/2  in. 
thickness  of  sleet  on  the  wires. 

NO.  o  STRANDED  COPPER 


Spans  in  feet 


IOO 

Temp. 

or  less 

125 

150 

200 

250 

300 

400 

500 

600 

•  ' 

Sags 

in. 

in. 

in. 

in. 

in. 

in. 

ft. 

ft. 

ft. 

0° 

2 

4 

6 

ii 

23 

40 

8£ 

i<5| 

29 

30° 

2 

4 

7 

13 

27 

46 

9 

17 

29^ 

60° 

3 

5 

9 

15 

32 

52 

10 

IT* 

30^ 

90° 

3 

7 

ii 

19 

37 

59 

I0| 

i»i 

3i 

120° 

4 

9 

14 

23 

42 

67 

»i 

J9 

31* 

490 


AMERICAN  TELEGRAPH  PRACTICE 

NO.  2/0  STRANDED  COPPER 


Spans  in  feet 

Temp. 

IOO 

or  less 

125 

150 

200 

250 

300 

400 

500 

600 

Sags 

in. 

in. 

in. 

in. 

in. 

in. 

ft. 

ft. 

ft. 

0° 

2 

3 

5 

10 

18 

30 

6 

"i 

IP! 

30° 

2 

4 

6 

ii 

22 

37 

7 

Mi 

201 

60° 

3 

5 

7 

13 

26 

44 

7^ 

13* 

aii 

90° 

3 

6 

9 

16 

31 

5i 

8i 

14 

22 

120° 

4 

7 

ii 

19 

36 

58 

9 

15 

23 

NO.  3/0  STRANDED  COPPER 


Spans  in  feet 

Temp. 

IOO 

or  less 

125 

150 

200 

250 

300 

400 

500 

600 

Sags 

in. 

in. 

in. 

in. 

in. 

in. 

in. 

ft. 

ft. 

0° 

2 

3 

4 

9 

15 

24 

56 

9 

isi 

30° 

2 

4 

5 

10 

18 

30 

64 

gi 

i6£ 

60° 

3 

5 

6 

12 

22 

36 

73 

iof 

17^ 

90° 

3 

6 

8 

14 

27 

43 

82 

II 

ifti 

120° 

4 

7 

10 

17 

32 

50 

92 

12 

19 

NO.  4/0  STRANDED  COPPER 


Spans  in  feet 


Temp. 

IOO 

or  less 

125 

150 

200 

250 

300 

400 

500 

600 

Sags 

in. 

in. 

in. 

in. 

in. 

in. 

in. 

ft. 

ft. 

0° 

2 

3 

4 

9 

12 

17 

39 

6£ 

I2| 

30° 

2 

4 

5 

10 

15 

21 

44 

7 

13! 

60° 

3 

5 

6 

12 

18 

26 

So 

8 

14* 

90° 

3 

6 

8 

14 

22 

31 

58 

8£ 

15* 

120° 

4 

7 

10 

17 

26 

37 

66 

9^ 

x6i 

APPENDIX  B 

NO.  2/0  STRANDED  ALUMINUM 


491 


Spans  in  feet 

Temp. 

or  less 

125 

150 

200 

250 

300 

400 

500 

Sags 

in. 

in. 

in. 

ft. 

ft. 

ft. 

ft. 

ft. 

0° 

2 

13 

25 

4* 

6| 

n| 

23! 

38 

30° 

3 

15 

3i 

5 

7 

12 

24 

38* 

60° 

6 

iQ 

37 

si 

7i 

Mi 

*4i 

39 

90° 

ii 

25 

42 

6 

8 

13 

25 

39^ 

120° 

17 

32 

47 

6i 

8| 

tii 

25^ 

40 

NO.  3/0  STRANDED  ALUMINUM 


Spans  in  feet 


Temp. 

100 

or  less 

125 

ISO 

200 

250 

300 

400 

500 

600 

Sags 

in. 

in. 

in 

in. 

ft. 

ft. 

ft. 

ft. 

ft. 

0° 

2 

8 

15 

33 

5 

81 

19 

32 

45 

30° 

3 

10 

22 

42 

Si 

9 

i9i 

3*i 

4Si 

60° 

6 

15 

28 

5i 

61 

9i 

20 

33 

46 

90° 

ii 

21 

34 

58 

7 

10 

20^ 

33i 

47 

120° 

17 

28 

40 

64 

7i 

ii 

21 

34 

47i 

NO.  4/0  STRANDED  ALUMINUM 


Spans  in  feet 


Temp. 

or  less 

125 

150 

200 

250 

300 

400 

500 

600 

Sags 

in. 

in. 

in. 

in. 

in. 

ft. 

ft. 

ft. 

ft. 

0° 

2 

5 

10 

20 

40 

6 

15 

26 

37i 

30° 

3 

7 

18 

30 

So 

7 

16 

26^ 

38 

60° 

6 

ii 

25 

40 

59 

7i 

i6i 

27^ 

39 

90° 

ii 

18 

32 

48 

67 

8| 

?7i 

28 

39i 

120° 

17 

27 

30 

56 

75 

9 

18 

28£ 

40 

APPENDIX  C 


TELEGRAPH 

' 

Morse                             Continental 

A                     . 

CHARACTERS 

=1 

Morse 

T 

Continental 

B   .  -                ...                           ... 

u 

C                    ...                       . 

V 

D 

W 

E  ...  

"X 

F              „    .        „ 

Y                .... 

G- 

7 

TT 

& 

I 

1  ...     ..... 

J                                                ... 

K 

2 

L 

3 

, 

M 

4              .... 

N  ....                  .„      . 

5 

0                      .     ., 

6               

P    . 

7 

Q 

8 

9  

. 

s  .  .  ^  ,  .  . 

o 

Short  Numerals  Generally  Us 
1                                |3                              15 

ed  By  Continental  Operators 

\i                      .    IQ 

•  r                                                        • 
.0                                             

Morse                      Continental 

•1 

Phillips 

:    Colon                                              i               m     m 

*  —    Colon  Dash     .                                                                           -        

*              * 

*  * 

•  •         • 

—    Fraction  Line                                                           .                                  _ 

-   Dash 

-    Hyphen                                                                                                                          .  .  •   • 

'    Apostrophe                                                                            .   __                  ^_  . 

.  .  —  .      .  — 

£   Pound  Sterling          -    _    - 

/  Shilling                                                                                                                   .   .   o 

*  *     *  * 

d.    Pence         -                                                 -                                          __         _ 

*  * 

$    Dollars 

jjj    Cents 

~*  *  * 

:  "  Colon  Followed  by  Quotation 

[  ]  Brackets  •        .      '                                           _  _ 

Quotation  within  a  Quotation                            ,,       _,._..,        .    .,_.    ... 

End  of  Quotation                                                          ... 

•  •  —  .       —  —  •  ^— 

—  «  •  —  .       .  .    • 

End  of  Quotation  within  Quotation 

pprrpnt,                                                                __  — 

Capitalized  Letter 

*    * 

Ttalirs  or  TTnderline                                                      ,  __  .    .        .            .  . 

* 

492 


APPENDIX  D 
USEFUL  TABLES 

COIL-WINDINGS,  RESISTANCE,  AND  OPERATING  CURRENT  OF  TELEGRAPH 

INSTRUMENTS 


Instrument 

Resistance, 
ohms 

Turns  of  wire 

Gage  of  wire, 
B.  &S. 

Normal 
operating 
current, 
mil- 
amperes 

Single  line  relay  
Single  line  relay  

75 
150 

2,350  per  spool  
3,600  per  spool.  .  .  . 

29,  single  silk  
30,  single  silk  

80 
40 

Single  line  relay  
Sounder  

250 
10 

3,900  per  spool.  .  .  . 
i,  080  per  spool 

32,  single  silk  
24  cotton 

25 

Sounder  
Polar  relay  .  .  . 

150 

IOO 

3,500  per  spool.  .  .  . 
i,  600  per  section 

33,  single  silk  
29  single  silk 

50 
20 

Polar  relay  
Polar  relay  
Polar  relay  

2OO 
300 
£,OO 

1,400  per  section.  .  . 
i,  800  per  section.  .  . 
2  500  per  section 

32,  single  silk  
33,  enameled  
34  single  silk 

20 
20 
20 

Neutral  relay  
Neutral  relay 

60 

1,400  per  section.  .  . 
i  600  per  section 

30,  single  silk  
33  single  silk 

60 
60 

Transmitter  
Transmitter  

2O 
150 

1,240  per  spool  
3,600  per  spool 

26,  single  silk  
30  single  silk 

200 

CQ 

WIRE  GAGES 

BROWN.  &  SHARPE'S  GAGE 

The  B.  &  S.  Gage  is  standard  for  copper  wire  and  is  understood  to  apply  to 
all  cases  where  size  of  copper  wire  is  mentioned  in  any  wire  gage  number. 

By  referring  to  table  it  will  be  seen  that  in  the  B.  &  S.  Gage,  to  all  practical 
purposes,  the  area  in  circular  mils  is  doubled  for  every  third  size  heavier,  by 
gage  number,  and  halved  for  every  third  size  lighter,  by  gage  number. 

Every  tenth  size  heavier  by  gage  number  has  ten  times  the  area  in  circular 
mills. 

Every  10  B.  &  S.  Gage  wire  has  an  area  of  approximately  10,000  circular 
mils,  and  from  this  base  the  other  sizes  can  be  figured,  if  a  table  should  not  be 
at  hand. 

493 


494 


AMERICAN  TELEGRAPH  PRACTICE 


WIRE  GAGES 

Iron  wire  Mile  ohm  at  60°  Fahr.  is  4500  Ibs.  100%  pure. 

H.  D.  Copper  wire       "        "      "     "        "       "     859     "        "  " 


1 

S 

IRON 

gfi 

? 

IRON 

C 

13 

H.  D.  COPPER 

97-95%  Conductivity 

d)      CO 

•r    M 

•£  w 

.2    rt 

i  ii 

Weight, 

Resist- 

5 | 

SS 

Weight, 

Resist- 

S rt 

8  £ 

Weight,        Resist- 

g  O 

a 

Lbs. 

ance,  60° 

< 

Q 

Lbs. 

ance,  60° 

S  O 

Q 

Lbs. 

ance,  60° 

PQ 

Per  Mile 

F.  Ohms 

Per  Mile 

F.  Ohms 

Per  Mile 

F.  Ohms 

2*8 

825 

3 

258 

932 

4.99 

3 

229 

729 

6.38 

3 

229 

838 

.04 

4 

238 

787 

5.97 

4 

204 

578 

8.05 

4 

204 

665 

.32 

5 

220 

673 

6.98 

5 

182 

460 

IO.II 

5 

182 

529 

.65 

6 

203 

573 

8.20 

6 

162 

364 

12.79 

6 

162 

419 

.09 

7 

180 

450 

10.44 

7 

144 

288 

16.16 

7 

i-U 

331 

.65 

8 

165 

378 

12.43 

8 

128 

228 

20.41 

8 

128 

262 

3-35 

9 

148 

305 

15.41 

9 

114 

181 

25.71 

9 

114 

208 

4.22 

10 

134 

250 

18.80 

10 

102 

145 

32  .  10 

10 

102 

166 

5.28 

ii 

I2O 

200 

23.50 

il 

91 

"5 

40.47 

ii 

91 

132 

6.65 

12 

109 

165 

28.48 

12 

81 

91 

51.15 

12 

81 

105 

8.36 

13 

95 

125 

37.6o 

13 

72 

72 

64.65 

13 

72 

83 

10.55 

14 

83 

95 

49   47 

14 

64 

14 

64 

65 

13    29 

15 

72 

72 

65.27 

IJ 

57 

1  5 

57 

52 

16   78 

16 

16 

18 

18 

26 

42       58 

20 

32 

16 

53.63 

CLASSIFICATION  OF  GAGES 

In  addition  to  the  confusion  caused  by  a  multiplicity  of  wire  gages,  several 
of  them  are  known  by  various  names. 

For  example: 

Brown  &  Sharpe  (B.  &  S.)  =  American  Wire  Gage  (A.  W.  G.). 

New  British  Standard  (N.  B.  S.)  =  British  Imperial,  English  Legal  Stand- 
ard and  Standard  Wire  Gage  and  is  variously  abbreviated  by  S.  W.  G.  and 
I.  W.  G. 

Birmingham  Gage  (B.  W.  G.)  =  Stubs',  Old  English  Standard  and  Iron 
Wire  Gage. 

Roebling  =  Washburn  Moen,  American  Steel  and  Wire  Co.'s  Iron  Wire 
Gage. 

London  =  Old  English  (not  Old  English  Standard). 

As  a  further  complication: 

Birmingham  or  Stubs'  Iron  Wire  Gage  is  not  the  same  as  Stubs'  Steel  Wire 
Gage. 

GENERAL  USES  OF  VARIOUS  GAGES 

B.  &  S.  G. — All  forms  of  round  wires  used  for  electrical  conductors. 
Sheet  copper,  brass  and  German  silver. 


APPENDIX  D  495 

U.  S.  S.  G. — Sheet  iron  and  steel.  Legalized  by  act  of  Congress,  March  3, 
1893. 

B.  W.  G. — Galvanized  iron  wire.     Norway  iron  wire. 

American  Screw  Co.'s  Wire  Gage. — Numbered  sizes  of  machine  and  wood 
screws,  particularly  up  to  No.  14  (0.2421  in.). 

Stubs'  Steel  Wire  Gage.— Drill  rod. 

Roebling  &  Trenton. — Iron  and  steel  wire.  Telephone  and  telegraph 
wire. 

N.  B.  S. — Hard  drawn  copper.     Telephone  and  telegraph  wire. 

London  Gage. — Brass  wire. 

EQUIVALENTS  OF  WIRES— B.  &  S.  GAGE 

=  16-9  =  32-12  =  64-15 

=  16-10  =  32-13  =  64-16 

=  16-11  =  32-14  =  64-17 

16-12  =  32-15  

16-13  =  32-16  

=  16-14  =  32-17  

16-15  =  32-18  

=  16-16  '  

16-17  

16-18 


0000 

= 

2-0 

=  4-3 

=  8-6 

= 

ooo 

= 

2-1 

=  4-4 

=  8-7 

= 

oo 

= 

2-2 

=  4-5 

=  8-8 

= 

o 

= 

2-3 

=  4-6 

=  8-9 

= 

I 

= 

2-4 

=  4-7 

=  8-10 

= 

2 

= 

2-5 

=  4-8 

=  8-1  1 

= 

3 

= 

2-6 

=  4-9 

=  8-12 

= 

4 

= 

2-7 

=  4-10 

=  8-13 

= 

5 

= 

2-8 

=  4-1  1 

=  8-14 

= 

6 

= 

2-9 

=  4-12 

=  8-15 

= 

7 

= 

2-10 

=  4-13 

=  8-1  6 

8 

= 

2-1  1 

=  4-14 

=  8-17 

9 

= 

2-12 

=  4-15 

=  8-18 

10 

= 

2-13 

=  4—16 

i1 

= 

2-14 

=  4-17 

.... 

12 

= 

2-15 

=  4-18 

13 

= 

2-16 

=  4-19 

14 

= 

2-17 

.... 

15 

= 

2-18 

16 

= 

2-19 

.  .  .  .' 

.... 

496  AMERICAN  TELEGRAPH  PRACTICE 

CURRENT  REQUIRED  TO  FUSE  WIRES  OF  COPPER,  GERMAN  SILVER  AND  IRON 


B.  &S. 
gage 

Copper, 
amperes 

German 
silver, 
amperes 

Iron, 
amperes 

B.&S. 
gage 

Copper, 
amperes 

German 
silver, 
amperes 

Iron, 
amperes 

10 

333- 

169. 

IOI  . 

26 

20.  6 

10.  6 

6.22 

ii 

284. 

146. 

86. 

27 

17.7 

9.1 

5.36 

12 

235- 

120.7 

71.2 

28 

14-7 

7-5 

4-45 

13 

200. 

102.6 

63- 

29 

12.5 

6.41 

3-79 

14 

166. 

85.2 

50.2 

30 

10.25 

5-26 

3-n 

IS 

139- 

71.2 

42.1 

3i 

8-75 

4-49 

2.65 

16 

117. 

60.0 

35-5 

32 

7.26 

3-73 

2.  2 

17 

99. 

50-4 

32.6 

33 

6.  19 

3-i8 

1.88 

18 

82.8 

42.5 

25-1 

34 

5-12 

2.64 

i-55 

iQ 

66.7 

34.2 

20.2 

35 

4-37 

2.24 

i-33 

20 

58.3 

29.9 

17.7 

36 

3-62 

1.86 

1.09 

21 

49-3 

25-3 

14.9 

37 

3-o8 

1-58 

•93 

22 

41.2 

21.  I 

I2.S 

38 

2-55 

i-3i 

•77 

23 

34-5 

17.7 

IO-9 

39 

2.  2O 

1-13 

.67 

24 

28.9 

I4.8 

8.76 

40 

1.86 

•95 

.56 

25 

24.6 

12.6 

7.46 

APPENDIX  D 


497 


THERMOMETER  SCALES 


Centigrade        Fahrenheit 

Centigrade 

Fahrenheit 

Centigrade 

Fahrenheit 

100 

212.0 

1 
66 

150.8 

32 

89.6 

99 

2IO.  2 

65 

149.0 

3i 

87.8 

98 

208.4 

64 

147.2 

30 

86.0 

97 

206.6 

63 

145-4 

29 

84.2 

96 

204.8 

62 

143-6 

28 

82.4 

95 

203.0 

61 

141.8 

27 

80.6 

94 

201  .  2 

60 

140.0 

26 

78.8 

93 

199.4 

59 

138.2 

25 

77.0 

92 

197.6 

58 

136.4 

24 

75-2 

9i 

195.8 

57 

134-6 

23 

73-4 

90 

194.0 

56 

132.8 

22 

71.6 

.       89 

192.  2 

55 

131.0 

21 

69.8 

88 

190.4 

54 

129.  2 

2O 

68.0 

87 

188.6 

53 

127.4 

19 

66.2 

86 

186.8 

52 

125.6 

18 

64.4 

85 

185.0 

5i 

123.8                               17 

62.6 

84 

183.2 

50 

, 
122.  O                              l6 

60.8 

83 

181.4 

49 

120.2                               15 

59-o 

82 

179.6 

48 

118.4                               14 

57-2 

81 

177-8 

47 

II6.6                               13 

55-4 

80 

176.  o 

.  46 

II4.8                               12 

53-6 

79 

174.2 

45 

II3.0 

ii 

5i-8 

78 

172.4 

44 

III  .  2 

10 

50.0 

77 

170.6 

43 

109.4 

9 

48.2 

76 

168.8 

42 

107.6 

8 

46.4 

75 

167.0 

4i 

105.8 

7 

44-6 

74 

165.  2 

40 

I04.O 

6 

42.8 

73 

163.4 

39 

IO2.  2 

5 

41.0 

72 

161.6 

38 

ICO.4 

4 

39-2 

7i 

159.8 

37 

98.6 

3 

37-4 

70 

158.0 

36 

96.8 

2 

35-6 

69 

156.2 

35 

95-o 

I 

33-8 

68 

154-4 

34 

93-2 

0 

32.0 

67 

152.6 

33 

91.4 

Seventy-five  degrees  Fahrenheit,  or  23.8°  C.  is  the  standard  temperature  for  measuring 
electrical  resistances  in  submarine  cable  tests. 

Sixty  degrees  Fahrenheit,  or  15.5°  C.,  is  the  standard  temperature  for  measuring  the 
electrical  resistance  of  wire  for  general  telegraphic  purposes. 


32 


INDEX 


Absolute  units,  5 
Action  of  gravity  cell,  13 

of  condenser  as  static  compensator,  252 
"Added"  resistance  of   Field  quadruplex, 

298 
Aerial  cable  twisted  pair  rubber  insulated, 

453 

open  lines,  speed  of  signaling  over,  209 
Alphabets,  492 

elements  of,  207 

Alternating-current  generator,  phantoplex, 
396 

motors,  32 

source  of  power,  31,  176 
Amalgamation  of  zinc,  14 
Ammeters,  159 
Ampere,  9 

Ampere- turns,  26,  160 
Annunciator  board  connections,  358 

branch  office,  356 

differential,  357 

Needham,  360 
Anode,  n 
Armature,  29 

closed-coil,  26,  29 

drum-wound,  29 

dynamo  tor,  37 

lap-wound,  30 

open-coil,  29 

ring-wound,  29 

suspension  of  relay,  215 

wave-wound,  30 
Arresters,  lightning,  119 
Artificial  line,  252 

rheostat,  261,  327 
Atkinson  repeater,  227 
Auto-starter,  for  a.-c.  motor,  43 
Automatic  starter,  motor,  42 

telegraphy,  402 
Postal  system,  415 

transmitter,  406 
Auxiliary  power  switchboard,  68 

B-side  call  bells,  366 

"kick,"  309 
Balance,  capacity  or  static,  333 


Balancing  duplex,  331 

quadruplex,  331 

rules  Postal  Tel.  Co.,  336 

W.  U.  Tel.  Co.,  337 
Ballistic  galvanometer,  155 
Barclay  direct-point  repeater,  386 
Battery,  arrangement,  3-wire  system,  62 

at  one  end  of  line  only,  108 

at  both  ends  of  line,  108 

circuit  arrangements,  71 

closed  circuit  types,, n 

double  fluid  cells,  1 1 

duplex,  266 

intermediate,  43,  347 

internal  resistance  of,  166 

open  circuit  types,  n 

primary,  10 

required  to  operate  single  Morse  lines, 
112 

single  fluid  cells,  1 1 

switching  systems,  58 

testing,  159 
Baume  scale,  15 
Berry  pole-changer,  286 
Blavier  test,  177 
Bonding  cable  sheaths,  469 
Boosters,  64 
Branch  office  annunciators,  356 

combination  single  and  duplex  set,  390 

connected  with  main  office  duplex  over 
one  wire,  390 

control  of  direct-point  repeater,  387 
of  quadruplex  repeater,  388 

definition  of,  130 

instrument  arrangement,  352 

wiring,  352 
Bridge  balance,  332 

duplex,  267 

Wheatstone,  160 
Bridging  telephone  set,  433 
Bridle  wire,  466 
B.P.O.,  quadruplex,  329 
Brown  &  Sharpe's  wire  gage,  493 
Brushes,  dynamo,  30 
Bug-trap  neutral  side  of  quadruplex,  309 
Bunnell  key,  117 


499 


500 


INDEX 


Bus-bars,  68,  265 

Cable,   aerial,  rubber  insulated,  specifica- 
tions for,  462 

aerial  and  underground,  455 

office,  specifications  for,  463 

sheath  bonding,  469 

testing,  197 
Cadmium  cell,  21 
Call  box,  Gill  selector,  376 
Calorie,  7 
Capacity  balance,  333 

condenser,  164 

electrostatic,  89,  202 

inductive,  91 

unit  of,  8 

Carhart-Clark  cell,  21 
Cartridge  fuse,  41 
Cathode,  n 

Catlin  self-adjusting  repeater,  244 
Cell,  n 

bichromate,  18 

Carhart-Clark,  21 

Clark,  21 

dry,  20 

Edison-Lalande,  12,  19 

Fuller,  12,  1 8 

gravity,  12,  15 

Lalande,  12,  19 

Leclanche,  12,  17 

standard,  21 

Weston,  22 

C.  G.  S.,  system  of  units,  7 
Charge  on  conductors,  89,  202,  334 
Chemical  electricity,  i 

symbols,  12 
Choke  coil,  121 
Circuit  calculations,  72 

divided,  70 

efficiency,  212 

grounded,  70 

joint,  85 

metallic,  70 

shunt,  83,  86 
Closed-circuit  cells,  n 
Closed-coil  armatures,  26 
Codes,  telegraph,  492 
Co-efficient  of  temperature,  8c 
Coil  windings  of  telegraph  instruments,  493 
Collector  rings,  dynamo,  25 
Combination  repeater,  380 

sets  for  single  or  duplex  working,  390 


Common  battery  feeding  several  lines,  113 

Commutator,  30 

Composite  telephone  and  telegraph  circuit, 

442 

Compound  dynamo,  27 
Concentrated  circuit  annunciators,  359 
Condenser,  162 

bug- trap,  314 

discharge,  timing,  335 

in  connection  with  artificial  line,  253 

method  of  measuring  inductance,  103 

reading,  270 

signaling,  269 

testing,  342 
Conductance,  10 

leakage,  203 
Conductivity,  10 

Mattheissen's  standard  of,  79 

measurements,  190 

specific,  77 

Conductors,  2,  3,  76,  81 
Constant  of  galvanometer,  156 
Continental  alphabet,  492 
Continuity  preserving  transmitter,  250 

tests  of  line  wires,  196 
Conversion  factors,  77 
Copper  wire,  conductivity  of,  494 

diameter  mils,  494 

resistance  of,  494 

specifications,  449 

weight  per  mile,  494 
Core,  100 
Coulomb,  9 

Counter  e.m.f.,  inductive,  103 
Cross-bar  switchboards,  134 
Cross-connecting  frame,  143 
Cross-fire,  209 
Cross,  location  of,  173 
Current,  4,  9 

of  charge  on  line  wires,  334 

proportions  in  quadruplex  circuits,  '299 

ratio  in  quadruplex  circuits,  299 

rectifiers,  54 

regulation,  dynamo,  45 

required  to  fuse  wire  of  various  gages, 
496 

unidirectional,  25 

values  in  telegraph  relays,  etc.,  436 

d'Arsonval  galvanometer,  154 
Davis-Eaves  quadruplex,  304 
Decrement  quadruplex,  314 


INDEX 


501 


Depolarizer,  battery,  14 
Derived  mechanical  units,  5 
Diehl  bug- trap,  313 

Difference   of    balance    pole-changer    key 
closed  and  open,  339 

of  potential,  4 
Differential  annunciator,  357 

bug- trap,  314 

galvanometer,  155 

neutral  relay,  289 

relay,  251 

winding  of  polar  relay,  259 

of  repeater  relay,  224 
d'Humy  tape  reperforator,  416 

self-adjusting  repeater,  243 
Diplex,  290 
Direct-point  repeater,  383 

branch  office  control,  of,  387 
Distributing  frames,  151 
Distribution  of  current  in  divided  circuits, 

114 
Disturbances  induced  in  telegraph  lines  from 

a.-c.  lines,  424 
Divided  circuits,  70,  114 
Double-fluid  cell,  1 1 
Dry-cell,  20 

used  to  operate  open-circuit  telegraph 

system,  no 

Ducts  in  operating-room  floor,  148 
Duplex,  249 

balancing,  331 

battery/  266 

bridge,  267 

city  line,  276 

double  current,  254 

high  efficiency,  273 

high  potential  leak,  272 

polar,  255 

Postal  system,  275 

repeater,  383 

short  line,  278 

single  current,  249 

Stearns,  249 

Western  Union,  271 
Dynamo,  23 

commutator,  25 

current  regulation,  45 

feeding  several  lines,  115 

field-magnet  winding,  24,  25 

magnetic  circuit,  27 

quadruplex,  295 
Dynamo  tor,  36 


Dynamotor  switchboard  wiring,  59 

Earth  connections,  128 

currents,  167 

potentials,  167 
Edison-Lalande  cell,  12 

Nickel  Iron  storage  cell,  53 
Effects  of  temperature  upon  resistance  of 

wires,  80 

Electric  charge  on  line  conductors,  334 
Electrical  measuring  instruments,  153 
Electrolysis,  467 
Electrolyte,  storage  battery,  50 

specific  gravity  of,  52 
Electrolytic  rectifiers,  55 
Electromagnets,  26,  96 
Electromagnetic  induction,  92 

units,  5 

Electromagnetism,  96 
Electromotive  force,  4,  9 
Electron  theory,  VII 
Electrophorus,  i 
Electropoin  fluid,  19 
Electrostatic  capacity,  202 
of  conductors,  89,  91 

flux,  202 

induction,  92 

from  passing  clouds,  120 

units,  5 
Energy,  electric,  10 

kinetic,  3 

potential,  3 
Erg,  99 

Escapes,  location  of,  177 
Exploring  coils,  198 
Extra  current  of  self-induction,  279 

Fall  of  potential,  87 

Fault-finders,  197 

Fault  location  in  cable  conductors,  176 

in  quadruplex  apparatus,  341 
Field  excitation  of  dynamos,  26 

key  quadruplex,  295 

rotating  magnetic,  32 
Figure  of  merit  of  relays,  215 
Fisher  loop  test,  177 
Flux,  electrostatic,  202 

magnetic,  8,  100 
Frictional  electricity,  i 
Force,  electromotive,  4 

magnetomotive,  8 
Freir  relay,  315 


502 


INDEX 


Fuller  cell,  12 
Fundamental  units,  5 
Fuse,  enclosed,  40 

wire,  41 
Fuses,  126 

in  motor  circuits,  40,  41 
Fusing  current,  wire  of  various  sizes,  496 

Galvanized  iron  wire,  specifications,  450 
Galvanometer,  153 

d'Arsonval,  155 

Ballistic,  155 

differential,  155 

in  quadruplex  circuit,  329 

shunts,  156 

used  as  low-reading  voltmeter,  469 
Gerritt  Smith  quadruplex  arrangement,  312 
Ghegan  repeater,  229 
Gilbert,  99 
Gill  selector,  369 

call  box,  370 
Gravity  battery  calculations,  75 

quadruplex,  292 

cell,  12 
Ground  coil  in  quad,  circuit,  302 

contacts  on  lines,  location  of,  172 

wires,  128 
Grounded  circuit,  70 

line  telephone  circuit,  432 

telephone  circuit  connected  with  metal- 
lic circuit,  434 

Half-deflection  method  of  measuring  resist- 
ance, 157 
Half-  repeater,  375 

Milliken,  381 

Hard  drawn  copper  wire,  449 
Heat,  effect  of  upon  resistance  of  wires,  80 
Helmholtz's  law,  94 
Henry,  10 
High  potential  leak  duplex,  272 

tension  line  crossings  above  telegraph 

lines,  473 

Holding  coils  of  neutral  relays,  317 
Horse-power,  7,  10 
Horton  repeater,  238 
Hot-wire  meters,  158 
House  circuit  repeater,  382 
Howler  telephone  signal,  443 
Hydraulic  analogy  of  electrical  action,  3 
Hydrometer,  15,  1 6 
Hysteresis,  100 


Impedance,  95 

of  receiving  instruments,  212 

of  retardation  coil,  435 

coil  simplex,  437 

coil,  W.  U.  quad.,  321 
Increment  key,  B.P.O.,  quad.,  329 
Inductance,  10 

a  factor  of  "time-constant,"  102 

in  electric  circuit,  205 

measurement  of,  103 

of  polar  relays,  214 
Induction  motor,  3  2 
Inductive  capacity,  8 

of  conductors,  91 

disturbances  from  a.-c.  lines,  424 

reactance,  435 
Inductorium,  317 
Insulation  resistance  of  condensers,  165 

of  line  wires,  184 
Insulators,  3,  431 

transposition,  431 
Iron  wire,  diameter  mils,  494 

mechanical  and  electrical  requirements, 

4Si 

resistance  of,  494 

specifications,  450 

weight  per  mile,  494 
Intermediate  battery,  42 

offices  on  single  lines,  1 08 

Morse  loop  connected  into  duplexed 
line,  392 

test  office,  130 
Internal  resistance  of  battery,  73 

of  quadruplex  apparatus,  298 

J-hooks,  431 

Johnson  coil,  282 

Joint  resistance  of  circuits,  82 

Jones  quadruplex,  295 

Joule,  7 

Kelvin's  method  of  measuring  resistance  of 

galvanometer,  157 
Key,  Bunnell,  117 
Keyboard  perforator,  406 
Kilovolt,  9 
Kinetic  energy,  3 
Kleinschmidt  perforator,  407 
KR  law,  205 

Lag  of  magnetization  behind  current,  101 
Law  of  shunts,  84 


INDEX 


503 


Lead  covered  aerial  and  underground  satu- 
rated paper  cable,  455 

Leak  resistance  of  Field  quad.,  298 

Leakage  conductance,  203 

Leclanche  cell,  12 

Leg-board    connections,     direct-point    re- 
peater, 384 
duplex  repeater,  branch  office  control, 

.       389 

Leg-boards,  344 
Legs  to  branch  offices,  353 
Life  of  gravity  battery,  1 7 
Line  capacity  too  high  to  be  balanced  with 
total  capacity  of  condensers,  340 

resistance  box,  W.  U.,  quad.,  326 
Lines  of  force,  97 
Lightning  arresters,  121 
location  of.  1 24 

disturbances,  119 
Local  circuits,  single  lines,  108 
multiplex  sets,  265 

connections,  W.  U.  quad.,  351 
Lodestone,  i 
Long-end  current,  295 
Loop-boards,  344 
Loops  to  branch  offices,  352 
Loops  witch,  Western  Union,  350 
Loop  tests,  173 
Loss  in  transmission  efficiency,  cables,  206 

Magnet,  electro,  104 

permanent,  2 
Magnetic  field,  205 

flux,  8,  100 

induction,  8 

leakage,  104 

moment,  8 

reluctance,  8 

saturation,  98 

units,  5 

Magnetomotive  force,  27,  28,  99 
Main-line  call  bells,  366 

switchboards,  130 
Make  spark,  284 
Mallet  perforator,  403 
Mattheissen's  standard  of  conductivity,  79 
Measuring  distant  quad,  battery,  342 
Mechanical  units,  5 
Megohm,  9 
Metallic  circuit,  70 

composite,  443 

quadruplex,  308 


Microfarad,  10 

Mile-ohm,  77 

Milliammeter  in  quad,  circuit,  327 

Milliken  repeater,  236 

half-repeater,  381 
Mirror  galvanometer,  154 
Morse  alphabet,  492 
Motors,  alternating  current,  32 

compound,  31 

direct  current,  30 

series,  31 

shunt,  31 

three-phase,  44 

two-phase,  44 
Motor  current  regulation,  37 

-dynamo,  35 

-generator,  34 

-starters,  a.  c.,  43 

d.  c.,  38,  41 

solenoid,  42 
Multiple  arrangement  of  cells,  72 

connection  of  relay  windings,  217 

-series  arrangement  of  cells,  73 
Multipliers  for  voltmeters,  158 
Murray  loop  test,  171 

Needham  annunciator,  360 
Negative  pole  to  line  on  closed  key,  340 
Neilson  repeater,  232 
Neutral  relay,  289 

with  holding  coil,  317 

with  short  cores,  317 

Western  Union,  320 
side  of  quad,  signaling  systems,  366 

O'Donohue  shunt  repeater,  391 
Office  cable  specifications,  463 

wire  specifications,  465 
Ohm's  law,  5 
"Ohmic"  balance,  331 
Open  circuit  cells,  1 1 

system  of  telegraphy,  no 
Oscillatory  discharges,  121 
Overcompounding  dynamo  winding,  28 
Overload  motor-starter,  41 

Paper  insulated  aerial  cable,  455 
Parallel  arrangement  of  cells,  74 
Perforated  tape,  410 
Perforator,  key-board,  406 

mallet,  403 
Periods  of  reversal,  317 


504 


INDEX 


Permanent  magnet,  2 

state,  91 

Permeability,  9,  98 
Phantom  telephone  circuit,  441 
Phantoplex,  395 

quad.,  398 

transformer,  400 
Pig-tail  cable  connections,  137 
Pin- jacks,  138 

connections,  loop-board,  349 

switchboard,  140 
Platinum  contact  points,  280 
Plugs,  double  conductor,  135 
Polar  duplex,  255 

operation,  262 
repeater,  385 
phantoplex-quad.,  398 
relay,  257 
inductance  of,  214 
windings,  214 
Polarity  of  magnet,  104 

of  solenoid,  97 
Polarization  of  cells,  14 
Pole-changer,  255 

of  Wheatstone  automatic,  409 
Porous  cup,  17,  1 8 
Postal  automatic,  415 

receiver    and    transmitter    circuits, 

421 
tape  take-up  gear,  420 

direct-point  repeater,  384 

dynamo  arrangement,  59 

gravity  battery  quadruplex,  294 

loopswitch,  348 

quadruplex,  local  circuits,  344 

repeater  instrument  rack,  394 

rules  for  balancing,  337 

spark  control,  283 
Potential  difference,  4 

energy,  3 

fall  of,  87 

leads,  60,  67 
Pothead  wire,  466 
Power,  unit  of,  7 
Power-board,  auxiliary,  68 

telegraph,  58,  65 
Primary  battery,  n 
Printing  telegraphs,  literature,  471 

systems,  422 
Proportion  of  currents  in  quad,  circuit,  299 

Quadruplex,  287 


Quadruplex  battery  measurements,  342 

3-wire  system,  62 

B.  P.O.,  329 

decrement,  314 

Davis-Eaves,  304 

fault  location,  341 

Field  key  system,  295 

Gerritt  Smith  arrangement,  312 

Jones  system,  295 

local  circuits,  Postal  system,  344 
Western  Union,  328 
with  no-volt  battery,  347 

management,  339 

metallic  circuit,  308 

Postal  system,  3.04 

repeater,  388 

signaling  bells,  361 

single  dynamo  system,  306 

theory,  gravity  battery  system,  288 

Western  Union,  318 
operation  of,  323 
Quantity  of  electricity,  9 

Ratio  of  currents  in  Field  quad.,  299 
Reactance  of  retardation  coil,  435 
Reading  condenser,  270 

sounder,  quadruplex,  310 
Recorder,  Wheatstone,  403 
Rectifiers,  electrolytic,  55 

mercury-arc,  54 
Relay  armature  suspension,  215 

characteristics,  214 

differential,  251 
neutral,  289 
winding,  259 

Freir  neutral,  315 

Morse,  109 

Neutral,  W.  U.,  320 

phantoplex,  396 

polar,  257 

repeater,  225 

single  line,  connections  of,  117 

windings,  214 
Releasing  current,  203 
Reluctance,  8 

of  magnetic  circuit,  100 
Reluctivity,  9 
Remanence,  100 
Repeater  adjustments  and  management,  246 

Barclay  direct-point,  386 

combination  half-set  and  single  line,  380 

direct-point,  383 


INDEX 


505 


Repeater,  half-set,  375 

half-Weiny,  377 

house  circuit,  382 

instrument     arrangement     on     rack, 

Postal,  394 
table,  W.  U.,  393 

MiUiken  half-set,  381 
*  O'Donohue  shunt,  391 

quadruplex,  383 

station,  definition  of,  130 

self-adjusting,  243 

single-line,  219 

three-wire,  240 

Repeating  coil  method  of  tying  telephone 
lines  together,  434 

telephone,  447 

Repeating  sounder  bug- trap,  311 
Reperforator,  bearing  adjustment,  419 

tape,  415 

Reserve  power,  32 
Residual  magnetism,  100 
Resistance,  4,  9 

added,  of  Field  quad.,  298 

affected  by  heat,  80 

joint,  82 

leak,  of  Field  quad.,  298 

measurements  of  line  wires,  175 

of  earth  contacts,  169 

of  lines,  76 

specific,  77 
Resistivity,  10 
Retardation,  202 

coil,  impedance  of,  435 

method    of    tying    telephone    lines 
together,  434 

coils,  telephone,  448 
Reversals  of  current,  291 
Reversing  key,  B.  P.  O.,  quad.,  329 
Rheostat,  artificial  line,  261 

motor  starting,  38 
Rotating  magnetic  field,  32 
Rotor,  32 

Saturated  paper  cable,  455 

Screening  telegraph  relays  from  inductive 

disturbances,  427 
Second    side  of    quad,   signaling  systems, 

366 
Selector  connected  into  duplexed  line,  371 

into  single  line,  372 

signaling,  368 
Self-induction,  in  line  wires,  205 


Self-induction     of     relay     balanced     with 

shunted  condenser,  217 
Semi-automatic  transmitters,  208 
Series-multiple  arrangement  of  cells,  73 
Series  telephone  set,  433 
Series-wound  generator,  26 
Several  lines  worked  from  a  single  battery, 

in 

Short-end  current,  295 
Shunt  circuit,  83 
Shunted  condenser,  217 
Shunt-field  winding  of  dynamo,  28 
Shunt,  galvanometer,  156 

repeater,  391 
Shunts,  law  of,  84 
Signaling  condenser,  269 

systems  for  quad,  circuits,  361 
Simplex  telephone  and  telegraph  circuit,  437 
Simultaneous  telephony  and  telegraphy,  434 
Single  dynamo  quad.,  306 
Single-field  dynamotor,  36 
Single  fluid  cell,  1 1 
Single  line  repeater,  219 

Atkinson,  227 

Ghegan,  229 

Horton,  238 

Milliken,  236 

Neilson,  232 

Toye,  231 

Weiny-Phillips,  222 
Single  Morse  circuit,  106 

phase  series  motor,  32 
Skirrow  switchboard,  139 
Solenoid,  96 
Sounder  circuit  B-side  of  quad.,  310 

single  line,  109 
Spark  at  contact  points,  279 
Specific  conductivity,  77 

gravity  of  electrolyte,  15 

of  storage  battery  electrolyte,  52 

inductive  capacity,  8 

resistance  of  conductor,  77 
Specifications  for  iron  and  copper  wire,  449 
Speed  of  signaling,  201 

related  to  receiving  end  impedance,  213 

over  aerial  lines,  209 

through  cables,  204 
Split-plugs,  135 
Spring  jacks,  136 

jack  connections  of  loop  board,  349 
Squirrel  cage  motor  connections,  45 
Standard  cell,  21 


506 


INDEX 


Starting  rheostat,  38 

Static  balance,  333 

Stator,  32 

Stearns  duplex,  249 

Storage  battery  discharging  circuit,  48 

Edison,  53 

for  telegraph  service,  47 

initial  charge,  50 

low  cell  indication  and  treatment,  51 

multiple  type,  47 

obtaining  additional  life,  53 

supplying  current  for  several  lines,  115 
Stranded  galvanized  steel  wite,  452 
Strap  and  disk  switchboards,  131 
Strength  of  received  signals,  211 
Submarine  cable  specifications,  456 
Sulphate  of  copper  solution,  14 
Superimposed  phantoplex  circuit,  398 
Susceptibility,  9 

magnetic,  96 
Switch-blocks,  140 
Switchboards,  cross-bar,  134 

main  line,  130 

pin-jack,  140 

strap  and  disk,  131 
Symbols,  5 
Synchronous  motors,  32 

Table  of  ratings,  storage  battery,  50,  53 
Tape,  perforated,  405,  410 

take-up  gear,  Postal  automatic,  420 
Telafault  test  set,  197 
Telephony,  432 

bridging  telephone  set,  433 
composite  circuit.  442 
condenser  capacities,  445 
terminal  connections,  445 

with    intermediate     telegraph 

station,  444 

with  no  intermediate  telephones,  444 
grounded  line  composite,  442 
connected  with  metallic  circuit,  434 
telephone  circuit,  432 
howler  signal,  443 
intermediate     station    on     composite 

line,  444 
telegraph     station    connected    into 

simplex,  439 

station  on  simplex  circuit,  438 
telephone    station    on    phantom 

circuit,  440 
and  telegraph  on  simplex,  439 


Telephony  metallic   circuit   composite, 

443 

metallic  telephone  line,  433 
phantom  circuit  transpositions,  440 

simplex  circuit,  441 

telephone  circuit,  439 
repeating  coils,  447 

coil  method  of  tying  lines  together, 

434 

retardation  coils,  448 
series  telephone  set,  433 
simplex,  bridged  impedance  coil  type, 

437 

transposition  of  telephone  lines,  428 
Temperature  co-efficient,  80 
Terminal  office,  definition  of,  130 
switchboard,  131 

resistance  of  quad.,  301 
Tests  with  telephone  receiver,  195 
Theory  of  electricity,  VII 
Thermal  electricity,  i 
Thermometer  scales,  496 
Three-phase  motor,  34,  44 
Three  wire  system,  62 
Time-constant,  101 

of  relays,  216 

Timing  condenser  discharge,  335 
Toye  repeater,  231 
Transfer  jacks,  149 
Transformer,  phantoplex,  400 
Transmission  efficiency  equivalents,  437 

losses,  206 
Transposition  insulators,  431 

of  wires,  428 
Transmitter,  automatic,  406 

duplex,  250 

quadruplex,  293 

repeater,  224 

semi-automatic,  208 
Twisted  pair  paper  cable,  aerial,  453 
Two-phase  motor,  44 

Underground  cable,  paper  insulated,  speci- 
fications, 455 

sheaths,  electrolysis  of,  467 
Underload  rheostats,  41 
Unidirectional  currents,  25 
Unit  strength  of  pole,  8 
Units,  5 

Vacuum  gap  arrester,  123 
Variable  state,  91 


INDEX 


507 


Varley  loop  test,  173 
Voltaic  cell,  1 2 
Voltmeter,  157 
tests,  182 

Walking-beam  pole-changer,  256 
Way-office,  definition  of,  130 
Wedges  for  use  with  spring  jacks,  136 
Weiny-Phillips  half-repeater,  377 

repeater,  222 
Western  Union  5-U  retardation  coil,  448 

bridge  duplex,  271 

direct-point  repeater,  386 

distributing  frame,  151 

dynamo  arrangement,  61 

instrument   arrangement   on   repeater 
tables,  393 

loopswitch,  350 

main-line  switchboard,  150 

proportional  test  set,  192 

quadruplex,  318 

local  connections,  328 

rules  for  balancing,  337 

signaling  system  for  multiplex  sets,  363 

spark  control,  283 
Weston  cell,  21 


Wheatstone  automatic,  402 
Wheats  tone  bridge,  160 
measurements,  170 

system,  mallet  perforator,  403 
recorder,  403 
transmitter,  406 

Windings  of  telegraph  instruments,  493 
Wire,  annunciator,  466 

bridle,  466 

call  circuit,  466 

gages,  493 

gages,  classification,  495 

hard  drawn  copper,  specifications,  449 

iron,  specifications,  450 

office,  specifications,  465 

outside,  twisted  pair,  466 

pothead,  466 

Wires,  telegraph,  crossing  under  high-ten- 
sion lines,  473 

Wireless  trouble  finders,  200 
Wiring   of   telegraph  power  switchboards, 

65 
Work,  unit  of,  7,  99 

Zinc,  12 

amalgamation  of,  14 


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